This study investigates the effectiveness of mathematics journals in improving the mathematics performance of Junior High School (JHS) students. A quasi-experimental design with a pretest-posttest control group approach was used, involving 60 students from two JHS classes. The experimental group used mathematics journals, while the control group received traditional instruction. Data were collected through pretest and posttest scores, analysis of journal entries, a survey questionnaire, and teacher observations. The results indicated that students in the experimental group showed significant improvements in problem-solving skills, conceptual understanding, and overall academic performance compared to the control group. The findings suggest that mathematics journals serve as an effective tool for enhancing students' engagement and learning outcomes in mathematics. Based on these results, it is recommended that mathematics educators incorporate journal writing into their teaching strategies to foster deeper understanding and improve performance.