This study examined the relationship between high school students' phonological awareness and their performance in pronouncing allomorphs of English inflectional morphemes -ed and -s. The study involved 31 high school students in Can Tho City in the Mekong Delta of Vietnam. Data of the study were collected through a pronunciation written test (PWT) and a pronunciation oral test (POT). The findings pointed out that all the students had phonological knowledge of the two morphemes; however, the majority of the participants made errors in pronouncing them which indicated their lack of pronunciation performance. In addition, there was no correlation between the students’ phonological awareness and their pronunciation performance detected in the study. Based on the results, pedagogical implications were suggested.