This study examined phonological factors affecting the intelligibility of English pronunciation among native speakers of Arabic learning English as a foreign language (EFL). In most cases, second language pronunciation is determined largely by the first language’s phonological system; this influence has been variously referred to as L1 interference or negative transfer. For learners of Arabic, since the differences between Arabic and English are quite marked with respect to their phonological features, there exist systematic and predictable patterns of mispronunciations which render comprehensibility difficult for both native and non-native interlocutors with them in English. The primary aim that this study sought was major phonological differences between Arabic and English through an analysis of how these differences manifest systematically as common errors in consonants, vowels, stress and intonation; then consideration about their effect on clarity in oral communication. The study was descriptive-analytical in nature, and (20) Arab EFL learners were selected using purposive sampling. The major tool for data collection was a specially prepared word list containing English phonemes and phonological structures known to pose problems for Arabic speakers, the participants’ (Iraqi undergraduate students) reading of which was recorded, hence audio-recorded readings. The recordings were subsequently analyzed using both perceptual analysis by a control group, who listened for error patterns, and acoustic analysis using Pratt software that objectively measured phonetic properties. The results revealed the presence of regular, systematic errors in the production of English consonants that do not exist in Arabic, for example /p/, /v/, and /ŋ/; even extreme difficulty in distinguishing English short and long vowels-for instance, /ɪ/ versus /iː/- transfer of syllable-timed stress patterns from Arabic onto the stress-timed rhythm of English. Finally, this research offered pedagogical implications for EFL pronunciation teaching through focused practice and learner awareness, and suggested future study in Arabic-English comparative phonology.