This paper tests whether frication duration plays an important role in perceiving fricatives and affricates. In other words, whether the frication duration is an acoustic cue for distinguishing fricatives from affricates. For this purpose two types of experiments are carried out. In the first experiment two sets of stimuli are created by decreasing the frication duration of fricatives by 10ms, and in the second experiment two steps of stimuli are created by increasing the frication duration of affricates by 10 ms. The results of the present study show that frication duration is the primary acoustic cue in perceiving fricative/affricate distinction in Korean. In addition, the amplitude rise time and burst information appear to play secondary roles in perceiving the distinction by a series of perception tests.