Social emotional learning (SEL) programs have been found to be effective on multiple outcomes, but few empirical studies were conducted in the Chinese context. The present study aimed to develop a Chinese SEL program for elementary school students, examine its effects on students' social emotional skills and mental health, and explore which groups benefited more from the intervention. The current SEL intervention consisted of 12 scripted weekly lessons with a variety of instructional methods like discussions, videos, painting, writing, and role play. Four treatment classrooms (N = 181 students) and four control classrooms (N = 185 students) participated in the current quasi-experimental study. All students filled out the social emotional skills scale and the strengths and difficulties questionnaire before and after the intervention. Results showed that compared to the control group, treatment group students had significantly higher scores on self-awareness, relationship skills, and responsible decision making, and lower score on conduct problems after the intervention. Students with lower baseline self-awareness benefited more from the intervention. The overall effect size for the four-month SEL curriculum was approximately one-quarter of a standard deviation, inspiring educators to implement SEL curricula in the Chinese context. Contributions and limitations are finally discussed.