Abstract: Objective: This experiment was conducted to assess the use of low energy diet which contains β-mannanase (Hemicell® HT) for its ability to improve the gross energy digestibility, dry matter digestibility and broiler performance. Methodology:About 301 days-old hubbard broiler male chicks were procured from local hatchery and 180 chicks with mean body weight of 40±2 g were selected and randomly assigned to one of three dietary treatment consisting of Standard Ration (SR), low energy ration (LE) and low energy diet supplemented with β-mannanase (LE+E) divided into 18 experimental units of 10 birds each. Results: Results demonstrated that LE+E diet improved (p<0.05) average body weight from 14-42 days and feed conversion ratio from 1-35 days. Different treatments did not affect the feed intake and mortality of the broilers. European production index was improved in LE+E fed birds as compared to the LE. Slaughter parameters including dressing, carcass, thigh, abdominal fat and gizzard percentage were not affacted by the dietary treatments. However, breast meat percentage was higher in SR fed broilers. The dietary treatments did not affect dry matter and gross energy digestibility of broiler. Conclusion: The study was completed, concluding that β-mannanase supplementation in low energy diet had beneficial effect on the body weight, feed conversion ratio, European production index and had no effect on the dry matter and gross energy digestibility.