ABSTRACT This study was developed using meta-analysis to evaluate the effect of β-mannanase on both poultry and pig performance. Two databases were constructed using information from previous studies that evaluated the β-mannanase supplementation in diets for broilers (30 papers; 19,643 birds) and pigs (20 papers; 5,319 animals). The meta-analysis followed three sequential analyses: graphical, correlation, and variance-covariance. The effect of β-mannanase supplementation on performance considerably varied in both databases. Data analysis considering the study effect showed that β-mannanase supplementation did not influence feed intake. Diets supplemented with β-mannanase did not influence weight gain, but improved feed conversion (−1%) of broilers compared with the control group. Feeding pigs diets supplemented with β-mannanase improved weight gain (+5%) and feed conversion (−6%) compared with pigs fed non-supplemented diets. β-mannanase supplementation increased the digestibility coefficient of dry matter, crude protein, and energy in both species. The inclusion of β-mannanase also improved the metabolizable energy content in broiler diets and enhanced the digestibility of energy in pig feeds. Current results indicate that β-mannanase can be considered as an important tool for nutritionists who search for improved feed conversions and nutrient digestibility coefficients.