The perception of Japanese consonant length contrasts (i.e. short/singleton vs long/geminate) by native and non-native listeners was compared to examine the extent to which difficult foreign language (FL) sounds are processed accurately by native speakers of Korean (NK). Three NK groups differed in their experience with Japanese: non-learners, intermediate and advanced. Via the AXB task, the NK speakers' discrimination accuracy of Japanese consonant length contrasts was assessed and compared to that of a group of 10 native speakers of Japanese (NJ) who served as controls. On average, the NK advanced group did not significantly differ from the NJ group and outperformed the NK non-learner (but not the NK intermediate) group. The NK intermediate and non-learner groups did not differ from each other. However, regardless of experience with Japanese, the NK speakers may benefit from the first language (L1) laryngeal contrasts, associating L1 Korean fortis consonants with Japanese geminates. The NK advanced group appeared less affected than the other two NK groups by Japanese pitch accent patterns in their consonant length perception. The NK advanced learners' results demonstrate that it is possible for non-native speakers to acquire native-like discrimination of consonant length in adulthood.