Cross-linguistic research on the development of tense-aspect marking has revealed a strong effect of lexical aspect. But the degree of this effect varies across languages. Explanation for this universal tendency and language-specific variation is still an open issue. This study investigates the early emergence and subsequent development of four grammatical aspect markers in Mandarin, "-le" (perfective), "zai" (progressive), "-zhe" (durative), and "-guo" (experiential), in the longitudinal speech data of four children acquiring Mandarin Chinese. It was found that the emergence of grammatical aspect marking generally follows the predictions of the aspect hypothesis, perfective "-le" predominantly appearing with telic verbs, whereas progressive "zai" is almost exclusively used with activity verbs. However, the typological features of Mandarin also affect the early uses of "-le", which is used with stative predicates more frequently than predicted, and the input patterns play an important role in children's aspect marking. The results support a usage-based learning process in accord with a language-specific system of aspectual semantics, rather than a strong universal association of grammatical aspect and lexical aspect. (Contains 7 tables, 1 figure and 11 notes.)