The goal of the study was to compare chemical and physical parameters of the content of various gastrointestinal (GI) tract segments of adult beavers and to relate the obtained results to seasonal changes in the composition of natural diet. The study was conducted on 36 adult beavers originated from the natural environment that were captured in winter, summer and autumn. The obtained results demonstrated that pH, redox potential (Eh), dry matter (DM), short-chain fatty acids (SCFA) and distribution of food particles varied along the beaver GI tract during the year. The lowest value of pH was observed in stomach whereas the highest in the small intestine and cecum. The reverse pattern of changes was found for the value of redox potential. The research indicated that anaerobic conditions were predominant in the cecum and so contributed to development of microbial population. Also, the increase in the SCFA contents in the cecum and colon indicated that beavers belong both to hindgut fermenters as well as to the mixed moderate type animals. In summary, the obtained results indicated that seasonal changes in the diet composition affected physical and chemical parameters as well as microbial activity of the GI tract of beaver.