Although the theoretical distinction between implicit and explicit knowledge of a second language has long been recognized,minimal documented description exists of the development of the two types of knowledge in L2 learners due to the difficulty in finding separate measures of the two types.To address this gap,this study first investigated the construct validity of the four tests developed by R.Ellis(2005)intended to distinguish between the two knowledge types:anoral imitation test,a timed grammaticality judgment test(G J T),an untimed GJ T and a metalinguistic knowledge test.The four tests,all examining 17 English grammatical structures,were administered to 88 native speakers of Chinese studying English as their major at the first three year levels in a Chinese university.The results from a confirmatory factor analy sis(CFA)confirmed the two-factor solution for the implicit/explicit model proposed in R.Ellis(2005).Repeated measures ANOVA was then used to reveal develop mental trends of the two knowledge types in the EFL learners across the three y ear levels.The results showed that learners at higher year level(or higher proficiency level)generally had higher level of both implicit and explicit knowledge of grammatical structures,and overall,the Chinese EFL learners possessed hig her level of exp licit knowledge than implicit knowledge.With regard to individual grammatical structures,the results of this study confirmed R.Ellis(2006b)finding that the level of difficulty of grammatical structures varied according to whether it was implicit or explicit knowledge of the structures involved. Although the theoretical distinction between implicit and explicit knowledge of a second language has long been recognized, minimal documented description exists of the development of the two types of knowledge in L2 learners due to the difficulty in finding separate measures of the two types.To address this gap, this study first investigated the construction validity of the four tests developed by R. Ellis (2005) intended to distinguish between the two knowledge types: anoral imitation test, a timed grammaticality judgment test (GJT), an untimed GJ T and a metalinguistic knowledge test. the four tests, all examining 17 English grammatical structures, were administered to 88 native speakers of Chinese studying English as their major at the first three year levels in a Chinese university.The results from a confirmatory factor analy sis (CFA) confirmed the two-factor solution for the implicit / explicit model proposed in R. Ellis (2005). Repeated measures ANOVA was then used to reveal develop mental trends of the two knowledge types in the EFL learners across the three y ear levels. The results showed that learners at higher year level (or higher proficiency level) generally had higher higher of both implicit and explicit knowledge of grammatical structures, and overall, the Chinese EFL learners possessed hig her level of exp licit knowledge than implicit knowledge. Whith regard to individual grammatical structures, the results of this study confirmed R.Ellis (2006b) finding that the level of difficulty of grammatical structures varied according to whether it was implicit or explicit knowledge of the structures involved.