The purpose of the present study is two-fold. First is to propose that an L1 (host language) speakers’ perception of L2 (donor language) sounds is conditioned by the acoustic cues to the laryngeal features of the L1 grammar in the loanword adaptation of Korean voiceless stops into Japanese and of the Japanese voicing contrast and voiceless geminates into Korean. Second is to suggest the enhancing role of some L2 or L1 phonetic properties in perceiving L2 variant(s) as distinctive according to the system of L1 features in loanword adaptation.