In this study the perception of word juncture in English and Arabic is investigated. Word juncture is taken as the allophonic, or phonetic, variation at word boundary that is contrastive. It is hypothesized that minimal pairs differentiated by means of juncture ( or boundary features) cannot be identified when heard in isolation and that the sentential context helps identifying the phrases of the pair. Corpuses of English and Arabic minimal pairs of juncture phrases were collected and native speakers of English and Arabic were asked to pronounce these phrases in isolation and then to use them in sentences. Three groups of subjects (a group of 13 Undergraduate students of English, a group of 11 MA students of English and a group of 9 Lecturers, all being native speakers of Arabic) were chosen to carry out the experimental part of the study. Four perception tests were carried out: two on English and two on Arabic. These tests were designated to examine the subjects' precision in the identification of the juncture phrases when used in isolation and in sentences. The subjects' reliance on the phonetic cues to identify the juncture phrases when used in isolation was low and rather fluctuant between the groups and the two languages. The sentential context, on the other hand, has shown a significant influence on the identification responses of the subjects in the three groups and in both English and Arabic.