The aim of this study was to investigate the effects of 3-nitrooxypropanol (NOP) on gas production, rumen fermentation, and animal performances depending on animal type using a meta-analysis approach. A database consisted of data from 14 studies, 18 experiments and 55 treatments. The supplementation of NOP linearly decreased methane (CH₄) emissions [g/kg dry matter intake (DMI)] regardless of animal type and length of experimental period (beef, p < 0.0001, R² = 0.797; dairy, p = 0.0003, R² = 0.916; and long term, p < 0.0001, R² = 0.910). The total volatile fatty acids (VFA) concentration and the proportion of acetate, based on beef cattle database, were significantly decreased with increasing NOP supplementation (p = 0.0015, R² = 0.804 and p = 0.0003, R² = 0.918), whereas other individual VFAs was increased. Based on the dairy database, increasing levels of NOP supplementation linearly decreased proportion of acetate (p = 0.0284, R² = 0.769) and increased that of valerate (p = 0.0340, R² = 0.522), regardless of significant change on other individual VFAs. In animal performances, the DMI, from beef cattle database, tended to decrease when the levels of NOP supplementation increased (p = 0.0574, R² = 0.170), whereas there was no significant change on DMI from dairy cattle database. The NOP supplementation tended to decrease milk yield (p = 0.0606, R² = 0.381) and increase milk fat and milk protein (p = 0.0861, R² = 0.321, p = 0.0838, R² = 0.322). NOP is a viable candidate as a feed additive because of its CH₄ mitigation effects, regardless of animal type and experiment period, without adverse effects on animal performances.