This paper investigates the interaction of syllable contact and morphological structure in Sino-Korean, based on a corpus approach. Two phonological phenomena are specifically discussed in this paper: (a) nasalization of lateral /l/ and (b) nasality percolation. This paper focuses on the morphological structure of trisyllabic phrases (ABC) in Sino-Korean, especially AB+C, a left branching internal structure. The corpus is based on Dictionary of Standard Korean Pronunciation, from which 230 phrases are gleaned. The 230 phrases are divided into 24 subcategories according to the classification of C in the ABC structure. The results suggest that 98.70% of the corpus instances of lateral /l/ undergo nasalization when they contact preceding nasals. The only exceptions (1.3%) are attested in the syllable contact of -n#l-, in which lateral /l/ does not turn into nasal. Instead, lateralization as in -n+l- > -ll- takes place. To account for the nasalization of lateral /l/ in Sino- Korean, this paper suggests that nasal percolation and progressive assimilation are the main causes for the phenomena.