Study skills are the various internal/external techniques that students use when they learn self-directly. And their components are consisted of sefl-regulating skills, class-listening skills, task-solving skills, and test-processin sklls. The purpose of this study were to examine relationshils between study skills and academic achievement, to fine the differences in study skills according to academic achievement levels, and to fine the differences in study skills according to academic achievement levels, and fine the most important sub-study skills for improving academic achievement in the middle school. For the study, 471 students were sampled in Pusan, Korea. Males were 245, females were 225. All were 2nd grade students in the middle school. Tools used in this study was Study Skills Inventory (SSI) made by Byun(1993) and scores of Korea, math, social studies, science, English tested by National Curriculum Evaluation Associaion in Sep.9 , 1998. Data were analyzed by Pearson correlation analysis, t-test, and stepwise multiple regression. Results were analyzed as followings: Firtst, there were relationships(r=.48) between study skills and academic achievement(p<0..1). The relationship(r=.45) between Math and study skills was highest. Self-regulating skills had the highest relation with academic achievement. Second, there were differences between sub-study skills which influenced academic achievement in the main subjects. Specially, self-regulating skills influenced academic achievement in all the main subjects most highly. Third, There were no statically signiricant differences between sexes in using study skills. Fourth, There were differences between academic achievement levels in using study skills(