This paper focuses on English initial consonant cluster acquisition by Cantonese ESL learners in Hong Kong, in order to gain insights into learners' interlanguage phonology. As a phonological rule appears to neutralize liquids in participants' interlanguage clusters, it is argued that further research is required to examine Cantonese ESL learners' capacities to perceive English speech sounds and the potential impact of their perceptual on their production abilities. Both hypotheses make predictions about second language learning on the basis of implicational universals, but the former is also premised on the differences between the native and target languages. The study investigated Cantonese ESL learners' acquisition of English obstruent + nasal onsets and obstruent + liquid onsets as well as their acquisition of two-member onsets and three-member onsets. A total of twelve learners participated in the study. They were asked to perform four different speech tasks including the reading of a word list, the description of a series of pictures using isolated words, the reading of three passages, and a conversational interview. The participants' speech was recorded using a high-quality mini-disk recorder and transcribed by two raters. The results of the study show that the implicational relationships which hold between the different categories of onset clusters also hold for the interlanguages of the participants, and the predictions of the MDH and the ISCH are also borne out. Where no universal markedness relationships exist among different onset clusters, the inherent difficulty of a segment resulting from the phonotactic constraints of a learner's mother tongue remains the most important factor contributing to the overall level of difficulty of an onset cluster. It is also argued that, in the interlanguages of the participants, there exists a phonological rule which neutralizes liquids in clusters. Further research is needed to investigate the abilities of Cantonese ESL learners to perceive English speech sounds and the possible effects that their perceptual abilities may have on their production abilities