The research was aimed at determining the impact of the experimental oral administration of zearalenon on the uterus in bitches. The study was carried out on 9 sexually mature 1 to 3 year-old bitches that were divided into three groups: two experimental ones and a control group. The experimental animals were orally administered zearalenon at 25 μg/ kg BW (body weight) (group DI; n=3) and 50 μg/kg BW (group DII; n=3) throughout 100 days while the control bitches (group K; n=3) were administered placebo. After the period of 100 days, ovariohysterectomy was performed, and the uterine samples were submitted to histopathological and immunohistochemical examinations in order to determine the structure of the wall and the presence of PCNA antigen. In the experimental animals, the histopathological examinations revealed regressive lesions, such as degeneration and atrophia within the endometrium and myometrium, and local circulatory disorders, i.e. edema and extravasation. These lesions were not reported in the controls. In the bitches administered zearalenon, the tissues did not express any proliferative activity as determined by the presence of PCNA. It is assumed that, following the administration of zearalenon for 100 days orally to bitches, disruption of the structures within the wall of the uterus (i.e. degeneration, atrophy, edema, and extravasation within the endometrium and myometrium) develops. This research proves that zearalenon ingested by bitches may lead to dysfunction of the uterus and cause disruption of its structures.