This study was conducted to analyze how many errors in the use of inflection and derivational morpheme by applying peer feedback to the writing class whether it can help students in the process of analyzing their assignments. This study uses explanatory research in which quantitative and qualitative data, then the data are presented with a percentage diagram, then the result is described. To obtain more detailed information about peer feedback, the researchers conduct interviews, after which the data is transcribed and the results are described. This research was conducted on 4th-semester students with 5 participants. The result of this study shows that students make more errors in using inflection + s with a percentage of 40%, and in derivational morpheme, students make more errors in using adverb suffixes with a percentage of 50%. The result of students peer feedback shows that the students positive respond apply peer feedback in writing class, the students also agree and strongly agree because the students feel confidents, interactive, communicative when discussing whit their peers, but also the students need the teacher to motivate and company the students to make more confident with their correction.

Keywords: Peer Feedback; Error Analysis; Essay Writing; Derivation And Inflection Morpheme.