The purpose of the present study is to help the high school English teachers develop insights into communicative grammar instruction. In order to examine what the teachers do in their grammar instruction, the study analyzed five video-taped high school English classes. From the analyses it was found that despite all the efforts made by the educational policy to implement the communicative language teaching, the high school English teachers" grammar instruction today is hardly different from the traditional one. What the teachers basically do in their grammar instruction is to explain the grammar points, translate the sentences, and include some mechanical drills. Based on the findings, the study concludes that the high school English teachers lack knowledge and techniques necessary to teach the target language grammar more communicatively. It is suggested that in order to make their grammar instruction more effective in developing the communicative language ability in the students, the teachers need to reduce the time to explain grammar points and increase the time to engage the students in the meaningful use of the target structure. An example of the grammar instruction is provided to help the teachers.