Instructions
Turn the rat over onto its back and hold it in your palm. Secure the rat by gently pressing your thumb against its chest. Look closely at the area between its hind legs.
Do the same with a few more rats. Observe differences in the space between the genital protuberance and the anus. Note that the space is wider in the male than the female. The protuberance is larger in the male. Also, the testicles emerge well before sexual maturity.
Look at the abdomen. The rat is female if there are nipples; males have no nipples.
How Can You Tell a Rats Gender?
It is not difficult to tell the difference between male and female rats, or bucks and does, as they are called. The differences in their genitalia are evident from very early on, even before they are a week old. Rats become sexually mature when they are as young as 5 weeks old. If you are raising pet rats, it's important to sex them correctly and separate them early on in order to prevent unwanted litters.