Tannins are water-soluble polyphenols with anti-nutritional properties but when supplemented at a low dose to the diets may exhibit positive effect on ruminants. Owing to great group diversity, tannins demonstrate various biological activities. They form complexes with nutrients and so they are enable to affect digestion processes. Thus, the aim of the study was to examine the effect of two types of tannins on sheep pancreatic enzymes activity. In the experiment 6 ewe of the Coloured Merino breed, fitted with catheters to the common pancreatic-biliary duct and simple cannula to the duodenum were used. Sheep were divided into 3 feeding groups for crossover design (n = 2), and fed control diet (CON) and two experimental diets with dried lingonberry leaves (VVI) or oak cortex (QUE) in a dose of 3 g ∙ d^–1, as a source of condensed and hydrolysable tannins, respectively. Non-significant effect of tannins on pancreatic-biliary juice secretion and its protein concentration was observed. In sheep fed diets with QUE addition lipase activity was increased in comparison to animals receiving VVI. An upward trend in amylase and trypsin activity after tannins addition was also found. Enriching sheep diets with additives containing tannins slightly stimulated pancreas exocrine activity. However, the inhibitory effects of tannins on endogenous protein activity, similar to the digestive enzymes inhibitors action, cannot be excluded. So, further studies on precise defining the mechanism of tannins action on enzymes activity and digestion process in ruminants are necessary.