The diversity of trunk muscle morphology of Salamandridae occupying different habitats (aquatic: Pachytriton labiatus; terrestrial: Tylototriton kweichowensis and Salamandra salamandra salamandra) was examined. Trunk muscles were dissected, and muscle weight ratios were quantified. The terrestrial species have larger abdominal trunk muscles than the aquatic species do. In contrast, the lateral hypaxial muscles are larger in the aquatic species. The M. rectus abdominis profundus is located subjacent to the M. rectus abdominis in the terrestrial species. In the aquatic species, the ventral muscle is composed of the M. rectus abdominis alone. The lateral hypaxial muscles in the aquatic species are suited to lateral bending during underwater locomotion in the denser aquatic medium. Larger abdominal muscles may be used in supporting body weight against gravity in the terrestrial species. The function of the M. rectus abdominis profundus may be to support the M. rectus abdominis in the terrestrial species. These findings suggest a divergent evolution of trunk muscle characteristics within the Salamandridae, which correlate with both habitats and modes of locomotion.