@@ This paper investigates three questions: do the Mandarin-speaking children with Specific Language Impairment (SLI) have difficulties in the comprehension and production of Chinese negator bu (不) and mei (you) (没(有)), compared with two other control groups of children: TDAM children (Typically-Developing-Age-Matched group) and MLU (Mean Length of Utterance)-Matched children (MLU-Matched group); if there are difficulties for the Mandarin-speaking children with SLI, in which aspect do the difficulties exist: semantic differences of the two negators, syntactic collocation of the two negators or in both aspects; what are the possible grammatical deficits that cause the difficulties. The theoretical frameworks adopted are that of Feature Checking, according to which feature plays a determining role in processing sentences, and that of Principle B and Principle M (Li 2007)which specify the features of Chinese negator bu (不) and mei (you) (没(有)). Paired experiment-questions are designed.