wikiHow to Tell if a Mouse Is Male or Female

Two Methods:Looking at Anatomical DistanceUsing the Nipple Method

Sexing mice is important especially if you're a breeder, keeping a large number of mice, or just curious about the sex of your little furry friend. There are two main methods of telling apart male mice (bucks) from female mice (does) that require a keen eye and gentle handling of mice. You can sex a mice by looking at anogenital distance or the distance between the mouse's genital area and anus. Or observing whether or not your mouse has nipples. It's always best to know the sex of your mice so you can separate the males from the females and prevent unwanted pregnancies.

Method 1
Looking at Anatomical Distance

  1. Image titled Tell if a Mouse Is Male or Female Step 1
    Pick up the mouse gently from its cage. The best way to do this is to softly pinch the base of its tail to lift up the mouse enough to slide your hand underneath its body. Keep holding the tail while you lift the mouse out of the cage.
    • Remember you are much bigger than the mouse and an untrained mouse will be frightened of you. Never try to scoop it up from the cage or squeeze the mouse. It might jump out of your hand and hurt itself.
    • Alternatively, you can train your mouse to crawl into you hand. The easiest way to do this is to put your mouse's favourite treats in your hand to entice them to enter your hand. However, if this is your first time, it may take a while before your mouse trusts you enough to eat off of your hand.
  2. Image titled Tell if a Mouse Is Male or Female Step 2
    Position the mouse to view its genital area. Take the mouse by the scruff of its neck, and turn the mouse on its back. If it's not comfortable with that position, hold the animal in your hand with its rear end facing you. Then, holding onto the base of its tail, lift it so that the genitals are in clear view.
    • It's important to lift the mouse at the base of its tail and never to have all of its feet in the air. Have at least the mouse's two front legs touching a surface. If you hold the mouse by its tail and let it hang, you risk the chance of breaking its tail or even snapping its back. You don't want to harm the mouse or cause it any pain.[1]
    • Pinkies, or newborn mice, can get cold very fast. So only handle them for brief periods of time. They are also extremely fragile so avoid lifting them by the tail.
  3. Image titled Tell if a Mouse Is Male or Female Step 3
    Look at the distances between the anus and the genitalia. The anus is the opening directly under the tail. Depending on the age of the mouse, it can be quite obvious or too difficult to sex. Young mice are very difficult to sex and the anogenital distances between sexes can almost look the same, so don't feel silly if you sex them incorrectly.
    • It would be helpful to compare multiple mice side-by-side until you are able to see a difference in distances.
    • In some cases, you may not have more than one mouse or all the anogenital distances look quite similar. Consult a book on mice or search the internet for pictures or diagrams demonstrating the sex differences between mice. Many sources provide visuals of mice's sex differences in every stage of growth.
  4. Image titled Tell if a Mouse Is Male or Female Step 4
    Determine a mouse as female. A female mouse has a genital area that is much closer to the anus. The urethra is usually within about 14 inch (0.6 cm) on an adult mouse.
    • Females will have a vaginal orifice behind the urethra which may appear to look like a bump.
  5. Image titled Tell if a Mouse Is Male or Female Step 5
    Determine a mouse as male. A male mouse has a genital area much farther away from the anus than in females. You may also see its testicles if they are dropped. A good way to tell the difference between testicles and a female's urethra, is if there is a vaginal orifice or opening behind the bump.
    • You can also try to look for the presence of testicles. Adult male mice will have dropped testicles and can be quite obvious to spot. However, you may have to be patient, because a male mouse can withdraw his testicles into his body. One way to get a good look is to wait for the mouse to eat while 'standing' on the rim of its food bowl. Most of the time his testicles will descend during this position.[2] However, the absence of testicles does not necessarily mean a mouse is female. Other methods may need to used to confirm the sex of the mouse.

Method 2
Using the Nipple Method

  1. Image titled Tell if a Mouse Is Male or Female Step 6
    Position the mouse to view its stomach. Take the mouse by the scruff of its neck, and turn the mouse on its back in your hand. However, nipples may be obscured by fur on the mouse's stomach. Try to part the fur or feel the belly to see if you can spot the nipples.
    • It can be difficult to spot nipples on pinkies but with good lighting and an observant eye, you can spot nipples as early as three days after birth.
  2. Image titled Tell if a Mouse Is Male or Female Step 7
    Look for nipples to determine a mouse as female. Male mice do not have nipples. While female mice have 10 nipples and should look like little indentations. The most prominent nipples are the two by the genitalia.
    • Pregnancy is usually an easy visual determination of sex, as the doe's nipples will swell and drop, forming "saddlebags" around the hip area. However, not all mice will be as obvious, and for some, obese males may look just like pregnant females. Try gently palpating the "saddlebags". You might be able to feel distinct nodes, which are likely the pups.


  • Separate your mice by sex as soon as possible. If there are mice you are uncertain of their sex, put them in a third separate category to be sexed later on.
  • Don't breed female mice older than 8 months. They are considered elderly at this point and in most cases, death will be the result after or during pregnancy.[3]


  • Do not pick up mice by the tail. Hold them gently in your hand and handle them delicately.
  • Never breed a doe more than 3 times in their lifetime.
  • If you do not separate your mice by sex, unwanted pregnancies can happen quite quickly and as early as 4 weeks after birth. Having babies can be quite hard for mice and some females can die during childbirth.

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Categories: Mice and Rats