This thesis investigates how Mandarin focus intonation is realized in the production of English L2 learners by examining relevant measurements of its acoustic carrier, fundamental frequency (f0), and comparing the observed results with those of the native speakers. The experiment and comparative results show that the English L2 learners are able to realize focus by manipulating duration and pitch range of the syllable accordingly. At the same time, most of the subjects are able to realize lexical tones, though not equally proficient among the four tones, instead of substituting them with a pitch accent. Result of an individual subject resolves a controversy over English focus and confirms it as a pitch accent. This thesis not only fills in a gap in the study of SLA of Mandarin intonation, but also provides pedagogical implications for L2 instruction of Mandarin.