Abstract: Uterine lesions are considered to be one of the main causes of canine infertility However, few publications have evaluated their real impact in the bitch. Uterine histological results of 20 bitches with unexplained infertility are exposed in this study. A surgical biopsy was performed by coeliotomy in all of them, during the luteal phase in 75% of the cases. Three groups were de ned: bitches whose pregnancy was never con rmed (NCP), birches with pregnancy arrest (PA) and hypofertile bitches. Overall, 89.5% of the biopsies were abnormal. Most frequently found lesions were endometritis (31.5%), CEH (Cystic Endometrial Hyperplasia) (31.5%) and FGD (brosis with degeneration of the endometrial glands) (21%). These lesions were diagnosed isolated or associated with other abnormalities. Any infectious agent was not isolated in none of the cases. CEH and FGD might play an important role in infertility, while endometritis might be the primary cause for some of the cases and a consequence of the pregnancy arrest for others.