The aim of this study was to determine the expression of Ki-67 and PCNA proliferative antigens and the apoptotic index in dogs with various degrees of severity of inflammatory bowel disease (IBD), and to evaluate the applicability of these markers in diagnosing the disease. The study was performed on 28 dogs of different breeds, both sexes, with body weights of 10 to 20 kg, aged 2 to 10 years. The animals diagnosed with IBD were divided into four groups of 7 dogs each, including three groups characterized by various degrees of severity of IBD and a control group. The expression of Ki-67 and PCNA antigens was determined immunohistochemically, and the apoptotic index was expressed as the number of TUNEL-positive lamina propria cells in the duodenum, jejunum and the colon. Regardless of its form, IBD affected the expression of the analyzed proliferation markers and apoptosis in duodenal, jejunal and colonic mucosa, but most of the analyzed parameters were not correlated with the severity of the disease. The severity of IBD was correlated only with the expression of Ki-67 in duodenal villi. The results of the study point to the limited applicability PCNA and the apoptotic index in differentiating and evaluating the progression of IBD in dogs. The estimation of Ki-67 expression may be useful in the evaluation of the severity of IBD in dogs.