The present study reports the results of an acoustic study of nasal assimilation at word boundaries in Chinese-Korean interlanguage. Twelve Chinese learners of Korean and four Korean native speakers recorded obstruent#nasal sequences in noun compounds and verb phrases, and their different production patterns were examined in detail. While nasalization of the word-final obstruents occurred only in 11.7% of the obstruent#nasal sequences for the Chinese learners, the Korean native speakers showed complete nasalization of those sequences. However, there was small, but consistent effect of learning on the production of external sandhi in L2, because there were shown to be differences in the rate of nasalization between the two proficiency groups of Chinese participants. On average, the intermediate level learners nasalized the target stops at the rate of 16%, and the beginning level learners showed the 7% nasalization rate. In addition, it was found that the context difference such as noun compounds versus verb phrases does not influence the nasalization pattern across word boundaries.