This study attempted to investigate the extent to which phonological characteristics of Farsi interfere with Iranian ESL learners‟ intelligibility when they interact with Canadian native English speakers. Most Iranians who learn English as a foreign or a second language would face phonologically-based difficulties that affect their comprehensibility when they communicate with native speakers. This study utilized a sample of five Iranian ESL learners and five Canadian native speakers as participants. Through the study, Iranian ESL learners underwent an interview and were asked to read twenty paired sentences that contained missing vowels and consonants in Farsi, and ten sentences including consonant clusters aloud while being tape recorded. Then, Canadian native speakers were invited to listen to the tape and declare their degrees of perception accordingly. The findings demonstrated that the phonemes and consonant clusters which do not exist in the Farsi phonological system and the difference in syllabic construction of two languages caused difficulties for Iranian ESL learners to be comprehended to a varying degree.