This study investigated the grammar learning strategies of high school students and any effect of their usage of those strategies on grammar test scores. To understand different types of grammar learning strategies, the 148 students were asked to indicate their extent to which they use as to 16 statements concerning grammar learning. Their responses to the 16 Likert type scale instrument were factor analyze and the results identified four distinct dimensions of strategies: ‘reflecting on the pre-existing knowledge', 'asking for assistance', 'applying knowledge', and 'taking autonomous actions'. After the identification of the four types of strategies, their strategy scores were related to subjects' grammar test scores by the application of logistic regression analysis. The multi-variate statistics results indicated that students with lower scores on the grammar test actually used higher frequency of reflecting strategy than those subjects with higher scores on the test, which was contrary to researchers' expectations. The unexpected result was interpreted in terms of the dimension of declarative knowledge of grammar with which subjects whose grammatical competence has not established tend to be more exploratory in employing the strategy than those students who have already acquired those declarative grammar skills. With the clear item loading onto each factor, the instrument may be used for assessing high school students' grammar study strategies, a part of English learning behavior.