beta-Mannanase (Hemicell) is a unique enzyme-based feed ingredient that can hydrolyze beta-mannan, an antinutritional fiber in feed. Because soybean meal contains beta-mannan and its derivatives, addition of beta-mannanase may improve soybean-meal utilization. The purpose of this study was to evaluate the effect of beta-mannanase on performance of commercial Leghorns fed corn-soybean meal based diets. In this experiment, 3 diets were formulated. The metabolizable energy content for diet 1 (high-energy diet) was 2,951 kcal/kg, which was 120 kcal/kg higher than diet 2 (low-energy diet supplemented with beta-mannanase) and diet 3 (low-energy diet without beta-mannanase). Hy-Line W-36 hens (n = 720, 98 wk old) were randomly divided into 3 dietary treatments (16 replicates of 15 hens per treatment). The trial lasted for 12 wk. Overall average feed conversion of hens fed the low-energy diet supplemented with beta-mannanase was similar to that of hens fed the high-energy diet, and both were significantly lower than that of hens fed the low-energy diet without beta-mannanase. There were no significant differences in overall average egg production and egg mass among 3 dietary treatments for the 12-wk period. However, the addition of beta-mannanase significantly increased average egg production and egg mass of hens fed the low-energy diet from wk 5 to 8. There were no significant differences in feed intake, egg specific gravity, egg weight, mortality, body weight, and body weight variability among the 3 dietary treatments. beta-Mannanase supplementation improved energy utilization of corn-soybean layer diets and has potential to reduce the cost of practical laying hen diets containing beta-mannan.