The female dog vaginal epitelium, changes from 2-4 layers in thickness into a multilayered epithelium during the estrous cycle, by ovarian hormones influence. Vaginal citology is a useful mean for determining stages of the canine estrous cycle, determining the optimal time to present a bitch to a dog for mating and diagnose several reproductive disorders (Olson et al, 1984; Thrall & Olson, 1993). In this article the autors show the methods of preparing and interpreting a vaginal smear