To evaluate the possible interaction between tannins and the activity of exogenous feed enzymes, the effect of tannin supplementation on added phytase efficiency in pigs was studied. An extract of sweet chestnut (Castanea sativa Mill.) wood was used as the source of tannins. Thirty-six pigs were divided into five groups: control (no supplement), Phy (550 PU/kg, 0 g tannins), Phy+Tl (550 PU/kg, 1.1 g tannins/ kg), Phy+T2 (550 PU/kg, 2.2 g tannins/kg) and Phy+T3 (550 PU/kg, 4.5 g tannins/kg). The results proved that phytase supplementation in the Phy group significantly increased apparent P digestibility and balance, Ca balance, serum inorganic P concentration, significantly reduced serum Ca concentration, numerically improved apparent nitrogen digestibility and significantly increased the N balance. Compared with the Phy group, the addition of tannins significantly reduced apparent protein digestibility. The apparent crude ash digestibility in the Phy+T3 group was also reduced (P<0.08). The utilization of phosphorus and calcium was unaffected by tannin supplementation. In conclusion, the applied concentrations of tannins did not reduce the phosphorus-related efficiency of phytase action in growing pigs.