Purpose: The current investigation evaluated the extent to which early noun, verb, and adjective lexicon sizes predicted later grammatical outcomes in Mandarin-speaking children with and without late language emergence (LLE) using a parent report. Method: In Study 1, the parents of 24 Mandarin-speaking children with typical language filled out the toddler version of "Mandarin-Chinese Communicative Development Inventory--Taiwan" (MCDI-T) when these children were 24 and 36 months old. In Study 2, the parents of 23 children with LLE completed the same form when these children were 24, 36, and 48 months old. Noun, verb, and adjective lexicon sizes and grammatical complexity scores were computed from the MCDI-T form for each child. Results: Study 1 showed that verb lexicon size, but not noun or adjective lexicon size, at 24 months predicted grammatical complexity scores at 36 months for children with typical language. Study 2 revealed that noun lexicon size, but not verb or adjective lexicon size, at 24 months predicted grammatical complexity scores at 36 months for children with LLE. Noun lexicon size at 36 months was also the only significant predictor for grammatical complexity scores at 48 months in children with LLE. Conclusions: Noun and verb lexicon size differentially predicted later grammatical outcomes in young Mandarin-speaking children with and without LLE. The finding suggested that children with LLE may have approached grammatical learning differently from their typical peers due to the small verb lexicon size in the early phase of language development.