Body shape of fishes is an important indicator of habitat selection and swimming behavior. Carassin as a non-native fish in Iran has an ability to adapt to various environmental conditions of its habitats. This study was conducted to investigate the body shape phenotypic plasticity of Carassin in two lentic and lotic conditions using geometric morphometric method. A total of 67 specimens of Carassin were captured from the Sefidrood River and Alagol Lake by electrofishing. Left side of specimens were photographed using digital camera and fifteen landmarks points were digitized on two-dimensional images using TpsDig2. Landmark data after GPA, analyzed using DFA and Manova and the patterns of body shape differences between two populations were illustrated in wireframe graph. Results revealed significant differences between the body shape of two studied populations (P<0.0001). Results, also, showed that the Sefidrood population has larger body depth, head, and shorter caudal peduncle than those of Alagol Lake. Finding of this study could confirm phenotypic plasticity response of Carassin to environmental features. Because of a short period from introduction of this fish to Iranian freshwater ecosystems, environmental features of carassin's habitats should be considered as main factor leading the morphological divergence than genetic ones.