This study investigates the degree of categoriality and discrimination accuracy in the perception of the three-way contrast in Korean stops and affricates by Mandarin speakers. The participants for this study include 44 Mandarin speakers who differ in Korean proficiency level and a control group of 13 native Korean speakers. Perceptual accuracy is assessed through an AX discrimination and an identification task. The result indicates that L2 proficiency plays a significant role in non-native speech perception. Overall, Mandarin listeners with more Korean language proficiency respond to the contrasts more like native Korean speakers than those with less proficiency. However, Mandarin learners of Korean have more difficulty perceiving lenis than aspirated and fortis, while they have less difficulty distinguishing aspirated from lenis and fortis regardless of their proficiency level in Korean. This finding suggests that Mandarin learners rely solely on VOT, which is a primary cue in their native language, when differentiating the Korean contrast, whereas native speakers of Korean use both VOT and F0 to distinguish the contrast. In light of this observation, Mandarin speakers who learn Korean as a foreign language need to focus on both VOT and F0 in order to increase their accuracy in the perception of the Korean contrasts. (University of Toronto)