The current quantitative and acoustic investigation is an attempt to shed light on the production of English affricates by Libyan students at the Department of English – University of Tripoli. English post-alveolar affricates /tʃ/ and /dʒ/ have no equivalent in the sound system of Modern Standard Arabic or in the Libyan Dialect. According to the Markedness Theory and the Contrastive Analysis Hypothesis, these sounds will constitute a challenge for those learners whose mother tongue does not have these sounds. In order to empirically test these claims, eight Libyan University students in their pre-sessional semester (four females and four males) produced 52 target words (monosyllabic, disyllabic and polysyllabic) with /tʃ/ and /dʒ/ in initial, middle and final position. The aim is to see if the students will undergo the process of deaffrication (the deletion of the plosive component from the affricate). Another aim is to see whether the number of syllables and the position of the affricate within the word will have any influence on accuracy. Results show that both the position of /tʃ/ and /dʒ/ and the number of syllables with the target words have an influence on accuracy. The students employed the process of deaffrication more when the target sounds occurred in final position. In addition, as the number of syllables increased, the percentage of accurate pronunciations decreased. It is hoped that the findings of this study will benefit both: the teachers to adopt appropriate strategies when teaching these sounds, and students to focus more on the production of these sounds.