<p>Domestication is considered one of the most powerful evolutionary forces driving brain size reduction in animals, as observed when domestic species are compared with their wild conspecifics. This pattern is often attributed to the relaxed selective pressures associated with foraging and predator avoidance in domestic environments. In this study, we compared relative brain size between domestic and wild conspecific frogs, including the American bullfrog (<i>Lithobates catesbeianus</i>) and the black spotted frog (<i>Pelophylax nigromaculatus</i>), while controlling for body size. We found that domestic individuals exhibited significantly reduced brain sizes compared with their wild counterparts in both species. These findings align with domestication theory, which posits that reduced predation risk and human-provided resources in captive environments contribute to brain size reduction. We also found that domestic bullfrogs tended to show greater brain size reduction than domestic black spotted frogs. To our knowledge, this is the first empirical evidence demonstrating that domestication is a major factor driving brain reduction in frogs.</p>