Abstract This research aims to to find out (1) what Vietnamese phonological features appear in first-year EFL students’speech and (2) how such Vietnamese phonological features influence their speech. The data were collected by recording student-student interaction in a speaking class and the units of analysis were at the level of vowel and consonant phonemes. The data were transcribed ,and analyzed to see the phonological patterns appearing in first-year EFL students’speech.Then these recordings were given to three native speakers to listen to discover how many percents they could understand the students’ speech and what phonetic problems they recognized from what they had heard. The study involved a sample of 6 first-year students of Ton Duc Thang University all of whom studied in the same class, had the same level of English and were of the same age .The findings of the study indicated that most of first-year students had a tendency (1) to omit the ending sounds (2) to replace the dipthongs with the vowels; (3) to mispronounce consonant sounds (4) to leave out one or two consonants in a consonant clusters and (5) to insert sound redundancy.