The phonological modifications made to English loanwords in Modern Standard Arabic (MSA) have come as a response to cope with the phonetic and phonological constraints in MSA sound system. These adaptations of loanword pronunciation clearly reflect the areas and effects of phonetic and phonological interference between the two languages in contact. For this purpose, over than 300 of English words borrowed by MSA are analyzed. At the syllabic and prosodic level, mechanisms like cluster simplification, syllabic consonant conversion, gemination, etc. are found at work and by far systematic in MSA borrowings. Generally, it has been found that most of the regular adaptations at syllable level such as declusterization, syllabic consonant conversion, consonant lengthening and vocalic glide insertion, are motivated by linguistic constraints inherited in the phonological system of MSA rather than by extra-linguistic motivations.