Japanese adults have difficulty learning the English /r/-/l/ contrast, and it has been suggested that this occurs because /r/ and /l/ are similar to the Japanese flap category. The present experiment evaluated this similarity by finding best exemplars of these three consonants in a 5-dimensional acoustic space (F1, F2, F3, closure duration, transition duration) for native speakers of Japanese and English. The results demonstrated that Japanese flap was similar to /l/, but not /r/, for Japanese listeners. However, the flap and /l/ best exemplars of Japanese speakers were still significantly different (e.g., flap having a shorter closer than /l/), indicating that Japanese speakers maintained separate mental representations for these categories rather than using their L1 flap for both consonants.