The aim of the present study was to investigate and compare the effects of different types of zeolites and their contribution in the diet on polysaccharidases activity in the rumen of heifers. Natural and synthetic zeolites and their various amounts (2 and 4% dry matter) were used. The study was performed on 5 rumen-fistulated Jersey heifers in a 5 x 5 Latin square design with 5 dietary treatments (control, 2% natural zeolites – ZN2, 2% synthetic zeolites – ZS2, 4% natural zeolites – ZN4, 4% synthetic zeolites – ZS4) and 5 experimental periods. The samples of ruminal digesta were taken from animals before feeding and 3 h after feeding. The significant interactions of diet and sampling time were shown for cellulolytic (P = 0.005), xylanolytic (P = 0.050) and amylolytic (P = 0.044) activities. The addition of 4% ZN to the diet significantly increased pectinolytic activity in the rumen in comparison to control group (P = 0.035). Interestingly, an upward trend of amylolytic activity has been shown (P = 0.082) in ZN2 group. The incorporation of 2% ZS to the diet significantly increased cellulolytic activity compared to control (P = 0.020) and ZN2 diets (P = 0.002). It can be concluded that zeolites can act in the origin- and dose-dependent manner. An increased activity of carbohydrate-digesting enzymes can be related to buffering properties of zeolites, which create favourable conditions for the growth and development of microorganisms. Differences between zeolites action on studied parameters may be derived from their chemical composition and particle size.