Anecdotally, native Mandarin speakers have difficulty distinguishing between the “s” (as in sink) and the “th” (as in think) sounds as well as between the “a” (as in dad) and “ea” (as in dead) sounds. Here, 29 native English speakers, 52 native Mandarin speakers who live in China, and 34 native Mandarin speakers who have been living in an English language dominant environment were recruited to serve as participants. To assess the phoneme contrasts that may occur in native Mandarin speakers in China, and possible improvement in native Mandarin speakers living in an English environment, relative to Native English speakers living in America, a phoneme discrimination test was administered, three paired phonemes were used in the current study: /b/ paired with /p/ as a control pair, /æ/ paired with /ɛ/, and /θ/ paired with /s/. The results showed that native English speakers have significantly higher accuracy rates for the three paired phoneme discrimination tasks than the native Mandarin speakers who live in China. But there was no significant difference between the native English speakers and native Mandarin speakers who have lived in an English environment on the phonemes or words discriminations tasks.