In the past century, grammar instruction has aroused debate among scholars and instructors in the field of second language teaching and acquisition without absolute consensus. However, for the acquisition of Chinese grammar by adult L2 learners, there is wider acceptance that grammar should be taught due to the unique Chinese grammatical features. The issue in question is merely on how to teach Chinese grammar effectively. Hence, inspired by many other comparative studies on explicit and implicit instruction methods for teaching Western languages such as English, French, Spanish and so forth, the researcher conducted an empirical study to investigate the effectiveness of the two instruction methods on Chinese grammar acquisition. The current study consisted of two experiments, involving two target forms: Affirmative-Negative Questions (A-Not-A Questions) and the perfective aspect particle LE (了). The participants were beginning level Chinese language learners who studied Chinese as a second language in two class sections of the Elementary Non-intensive Chinese Class at a large public university. They formed two comparative groups naturally. During the two experiments, the explicit group was provided with explicit knowledge of grammar patterns, examples carrying the patterns and opportunities to practice with the teacher’s explicit corrective feedback, while implicit group received input without any grammatical knowledge or explanation. The teacher would give recast feedback (implicit) if students made mistakes in their practice. Importantly, the explicit and implicit teaching groups were reversed in the second experiment, in order to enable each group to be exposed to both the explicit and the implicit teaching conditions. Analysis of the results obtained from immediate-tests and delayed post-tests yielded three main findings: first, learners who had received explicit grammar instruction treatment overall gained greater improvement in their knowledge of, and their ability to use the target forms in the short term; second, when it comes to longer-term effects, both groups in the two experiments showed loss, in varying degrees, in the knowledge of and the ability to use the target forms; third, explicit instruction was of more advantage for L2 Chinese learners when they are learning more complex rules.