Chinese grass shrimp, Palaemonetes sinensis (Sollaud, 1911) were collected from inland waters of Nao-shima Island and Awa-shima Island, Seto Inland Sea, western Japan. The appearance of P. sinensis is thought to be due to the escape of imported shrimps used as sport fishing bait. P. sinensis looks conspicuously like the native freshwater shrimp, Palaemon paucidens De Haan, 1844. However, the two species have different eye sizes and differences in three diagonal stripes on the carapace. We provide a simple method using eye size and carapace color pattern to enable preliminary differentiation of the two species in the field.