This study accounts for the acquisition of English onset /s stop r/, /s stop/ and /stop r/ clusters by Chinese and Korean learners. Participants in this study include 10 low level and 10 high level Mandarin and Korean EFL learners each. The material includes 27 words of target clusters. The results show that Mandarin and Korean speakers tended to make more modification in the more marked tri-consonant clusters than the less marked bi-consonant clusters. In addition, high level subjects performed noticeably better than low level subjects in both groups. Korean and Mandarin speakers’ simplification strategies were different: Mandarin speakers inserted /u/ or /ə/ into the clusters, whereas Korean speakers preferred to replace one of the consonants (often /r/) with another consonant in tri-consonant clusters and /stop r/ clusters. Both Korean speakers and lower English proficiency Mandarin speakers mistakenly aspirated the voiceless stops /p, t, k/ in the onset /s stop/ clusters.