This article reports on an empirical study on the acquisition of Chinese imperfective markers ("zai," "-zhe[subscript P]" and "-zhe[subscript R]") by English-speaking learners at three proficiency levels. Compared to English, Chinese has a richer imperfective aspect in terms of markers (forms) and features (meanings). Results are presented from a grammaticality judgment task, a sentence-picture matching task and a sentence completeness judgment task. We find that advanced learners are successful in reassembling additional semantic features (e.g. the [+durative] feature of "zai" and the [+atelic] feature of "-zhe[subscript P]") when the first language (L1) and second language (L2) functional categories to which the to-be-added features belong are the same. However, advanced learners have problems in differentiating between the interpretations of the progressive "zai" and the resultant-stative "-zhe[subscript R]", and are not sensitive to the incompleteness effect of "-zhe[subscript P]", which indicates that discarding L1-transferred features is arduous for learners. Our findings, in general, support the predictions of the Feature Reassembly Hypothesis (Lardiere, 2009). In addition, there is some evidence obtained for L1 influence, which persists at an advanced stage.