English is used as a lingua franca throughout Asia, but with a wide degree of variation in production and perception. Since accentedness does not necessarily correlate with intelligibility (Munro & Derwing, 1995), segmental productions of Mandarin L1 and American English L1 speakers reading 60 English sentences from the Bamford-Kowal-Bench Standard Sentence Lists (Revised in American English) were measured and compared, revealing the most significant differences. Then, in a psycholinguistic word-recognition-in-noise experiment, these sentences were mixed with white noise at a +5 dB signal-to-noise ratio and presented as stimuli to American and Korean listeners, who transcribed the sentences they heard. Intelligibility was determined by comparing the three to four key words in each stimulus sentence to the listeners’ written transcriptions. Since all listeners were graduate students in the U.S. who were certified to teach at the university level, and the key words were highly familiar to native speakers of English, those words which matched exactly were scored as accurate, while those which did not were marked as inaccurate. In addition, the listeners rated their familiarity with known key words on an increasing 5-point Likert scale, while unknown words were entered as ‘0.’. A series of mixed effects models with logistic regression analyzed the effect of speaker segmental production accuracy and listener word familiarity on intelligibility. Individual speaker and listener variation, as well as key word variation, were crossed as random effects. For the Koreans, Mandarin-accented English was significantly less intelligible than for the Americans and the differences in the segments that most frequently caused problems for each L1 listener group lend evidence to the strong role played by perceptual foreign accent (McAllister, 1997) in English as a Lingua Franca (ELF) contexts. Word familiarity was also found to be a significant predictor of intelligibility, but speaker segmental production accuracy was not. Improving intelligibility for Chinese and Korean interlocutors in ELF contexts should therefore include a combination of phonetic training in listening and vocabulary building.