This article discusses the results of a study which investigated Cantonese ESL learners’ perception of English vowels and their perceived similarity between similar L1 and L2 vowels in an attempt to test the prediction of the Perceptual Assimilation Model (PAM). Forty university English majors participated in three L2 perception tasks, which aimed at discerning their perception of English vowels spoken in different contexts, and one L1 L2 speech perception task, which aimed at discerning their classification of L2 vowels into native vowel categories and their perceived similarity between similar L1 and L2 vowels. It was found that their classifications of English vowels into Cantonese vowels and their perception of the corresponding English vowels did not provide strong support for the prediction of the model. The effects and extent of native language phonological influence are yet to be determined.