The aim of this study is to investigate the effect of vowel context and language experience in the perceived similarity between L2 English fricatives and Thai sounds. The target English sounds being investigated were the sounds /v, f, w, ?, t?, s, ð, d, z, ?, t??/. These sounds were elicited from four native English speakers in words in onset position and followed by three vowel contexts: high, low and back. Subjects were 54 Thai students divided into two groups: English-major and non-English-major. These Thai learners were asked to identify the sounds they heard with the Thai sounds that were closest in their perception. The findings showed that 1) all shared sounds were matched with the same L1 categories, suggesting that the existence of L2 sounds in the L1 sound system supports the perception; 2) most non-shared sounds, except English /?/ were matched to Thai sounds that were suggested in previous literature; 3) the perceived similarity of English /?/ and the L1 Thai sounds showed the effect of the vowel context in that this sound was mostly matched with Thai /f/ in the high and low vowel contexts whereas in the back vowel context, it was matched with Thai /s/; 4) the perceived similarities of both shared and non-shared sounds were affected by vowel context and language experience. The findings of this study shed light on the importance exploring perceived similarities and differences in the phonetic level rather than the phonological one.