This experiment was conducted to investigate the effects of different supplemental levels of β-mannanase on broilers fed corn-soybean meal basal diet based on an in vitro digestion method. The digestibility of dry matter (DM), crude protein (CP) and energy of the diets supplemented with β-mannanase at 0, 300, 600, 1 200 and 2 400 U/kg was determined in vivo and in vitro, and the performance of the broilers was also determined. A correlation analysis was carried out additionally. The results of the in vivo experiment showed that compared with the control group, β-mannanase added into the basal diets at the levels of 300 to 2 400 U/kg could increase the digestibility of DM, CP and energy, and the highest digestibility of nutrients was achieved at the supplemental level of 600 U/kg. The results of the in vitro experiment had the same trend with the in vivo one. The results of the correlation analysis showed that the in vitro digestibility of DM, CP and energy had correlations with the the average daily gain of the broilers （R2=0.792 3, 0.860 9, 0.773 0）, and had a strong correlation with the ileal apparent digestibility of nutrients in broilers （R2=0.989 9, 0.907 3, 0.985 2）. These results indicate that the in vitro digestion method is suitable to evaluate the effects of β-mannanase supplemented to the corn-soybean meal diets on the performance and nutrient digestibility of broilers.［Chinese Journal of Animal Nutrition，2011，23（1）：130-135］