This study aims to explore the influence of integrating Social and Emotional Learning (SEL) into choral instruction on peer relationships among high school students through an action research approach. It examined the design and implementation of an SEL-integrated choral curriculum, students’ SEL and peer interaction outcomes following the instruction, as well as challenges and coping strategies observed during the teaching process.65 first-year students from two classes at a public girls’ high school in Taipei City participated in the study. The study was conducted over nine weeks and included nine lessons. The research centers on SEL-based choral instruction, using the Social and Emotional Learning and Peer Relationships Scale, the SEL Choral Course Feedback Questionnaire, teacher reflection journals, and peer teacher observation records as research instruments. Triangulation was employed to ensure the validity and reliability of the findings.The research findings are as follows:1. Curriculum Design: The SEL-integrated choral instruction was developed based on CASEL’s five core competencies and included activities such as vocal exploration, voice part practice, jigsaw cooperative learning, and stage performance practice. The curriculum effectively combined music learning with social-emotional processes, providing opportunities for students to develop self-awareness and group cooperation skills.2. Instructional Practice Process Promoted Classroom Interaction: The curriculum was implemented in two cycles. Through voice part grouping and cross-part jigsaw cooperative learning, students gradually shifted from passive withdrawal to active engagement. Students increasingly demonstrated communication, coordination, and emotional regulation skills. The teacher’s timely guidance clarified classroom tasks, fostered a supportive classroom atmosphere, and enhanced students’ motivation and class cohesion.3. Students’ Learning Performance Showed Positive Changes: Statistical data indicated significant progress in self-awareness, social awareness, and interpersonal skills, with the total SEL score showing highly significant improvement. Peer interactions also improved notably, and social anxiety related to choral activities decreased. In addition, student feedback indicated that the curriculum enhanced emotional expression, self-confidence, and a sense of group belonging, while also improving the quality of peer interactions and music learning outcomes.