Exogenous fibrolytic enzymes can be a feature to improve fiber digestion and performance of dairy cows. This study was aimed to evaluate the effect of exogenous fibrolytic enzymes on milk yield and composition. Twenty-four Holstein cows (180.2 ± 54.3 DIM; 662.6 ± 88.2 kg BW) were assigned in a replicated 4 × 4 Latin square design, with 21-d periods. Dietary treatments were: 0 (control), 8 (low), 16 (middle) and 24 (high) g of enzyme/cow/day (Fibrozyme, Alltech Inc., Nicholasville, KY) of total mixed ration based on corn silage. Milk yield was recorded by a computer twice daily at 0600 and 1600 h. Milk sample was collected proportionately to a.m. and p.m. milking, and analyzed for fat, protein and lactose by near infrared reflectance spectroscopy. Data were subjected to ANOVA and simple polynomial regression using the SAS software, version 9.0. There was no effect of fibrolytic enzyme supplementation on milk yield (30.24 vs. 30.22 vs. 30.52 vs. 29.89 kg/d) and 3.5% fat-corrected milk (FCM) yield (30.96 vs. 31.70 vs. 31.33 vs. 30.71 kg of 3.5% FCM/d) for control, low, middle and high supplementation, respectively. Also, milk composition was not affected (P > 0.05) by enzyme supplementation just like yield fat, protein and lactose. A possible explanation for these results is that animals were not with energy challenge. Results of present study indicated that the use of exogenous fibrolytic enzymes did not improve performance of mid-lactation dairy cows.