The purpose of this study is to explore ways that enhance the impact of peer feedback activities by analyzing the validity of feedback opinion types. This study categorized feedback opinions provided by peer students in rewriting and tried to find out the concrete aspects of the feedbacks. This paper analyzed 40 pieces of first drafts, feedback opinions, amended drafts of the 11th grade students' writing. The total number of peer feedback comments were 384 and four Korean teachers assessed validity of these feedback opinions. As a result, average validity was 72.7%. The result shows that peer feedback ensures the validity of more than a certain level. Meanwhile, as a result of the analysis by types, friendly feedbacks have more validity than critical feedbacks. Feedbacks to provide an alternative have more validity than vague and cursory feedbacks and ones to point out an error. Feedbacks on areas of expressions have more validity than feedbacks on contents and structures.