Acoustic analysis suggests that each of the following variables can cue the post-alveolar fricative-affricate contrast in isolated word forms in Persian: silence duration, frication duration, rise time and amplitude rise slope. The acoustic values of each cue differ with the position of the test item in the word. Silence and frication duration of Persian affricates was longest in the final position. The rise time of Persian voiceless affricate was also longest finally but the amplitude rise slope was longest initially. It is confirmed that there is a positive relation between frication duration and silence duration, frication duration and rise time and also silence duration and rise time. The trading relation between frication duration and amplitude rise slope was negative.