Instructions
Gently cup the hamster in the palm of your hand and flip it over so its belly faces up. If your hamster doesn't cooperate, place it in a clear container and look through the bottom of the container to inspect its underside.
Inspect the hamster's rear end and locate two small holes -- the hole nearest the tail is the anus, and the hole above is the genitalia. The holes are about 1 cm (about 2/5 inch) apart in male hamsters and close together or touching in female hamsters.
Inspect the area under the hamster's genital region for a tiny bulge. This is the male's scrotum. Female hamsters don't have this bulge.
Inspect the hamster's belly for nipples. Female hamsters have four tiny nipples on each side, which are absent in males.
How Can You Tell if a Hamster is Female or Male?
Hamsters use olfactory, or scent cues to distinguish between males and females. Since humans lack the ability to distinguish the subtleties of hamster pheromones, they must visually inspect their pets to determine their gender. Unless you plan to breed your hamsters, it is a good idea to segregate males and females to prevent unwanted babies. Once a hamster is 3 to 4 weeks old, you will be able to distinguish the two genders.