A two-factor experiment was conducted to evaluate the effect of varying dietary levels (10, 20 and 30%) of faba bean (FB; Vicia faba L.) seeds with high- and low-tannin content (HT and LT, respectively) on the gastrointestinal function and performance of turkeys during the last 6 weeks of rearing. In the control group (FB0), birds were fed maize-soyabean meal-based diets. In comparison with HT FB seeds, in LT seeds lower content of condensed tannins (0.78 vs 0.08% DM) was determined. Different dietary inclusion levels of HT and LT FB had no influence on feed intake or viscosity and pH of small intestinal digesta, and the pH of caecal digesta as compared with FB₀. In comparison with HT FB, LT seeds increased ammonia concentrations, decreased pH and reduced activity of microbial α-glucosidase in the caecal digesta. All diets containing FB stimulated the activity of β-glucuronidase in comparison with diet FB₀. In turkeys fed LT seeds the production of short-chain fatty acids (SCFAs) was higher than in birds fed HT FB. Body weight gains of turkeys were comparable in all groups, however feed conversion ratio was lower in groups fed LT than HT FB seeds. So, FB enhanced fermentation processes in the gastrointestinal tract of turkeys, but had no influence on their performance. Both LT and HT FB seeds can be included in finisher turkey diets (up to 30%) as an effective substitute for soyabean meal. FB with lower tannin content improved selected parameters of gastrointestinal function, including increased SCFA production in the caeca and so improved feed efficiency.