Although there is substantial evidence for the merits of integrating social and emotional learning (SEL) into educational settings, little empirical research on this learning approach has been conducted in Mainland China. We synthesized the frameworks of Western SEL and the guidelines of Chinese mental health education, and conducted a preliminary assessment of a short-term SEL curriculum that we designed and piloted in an elementary school. We randomly assigned two classes comprising 111 fifth-grade students to take the SEL curriculum (intervention group), and compared them with a third class comprising 53 fifth-grade students assigned the usual curriculum (control group). The results show that the intervention group had a significant increase in emotional intelligence scores after completing the activities in the curriculum, and the control group experienced an increase in feelings of competitiveness. Students in the intervention group generally perceived the SEL curriculum as striking the right balance between enjoyable activities and valuable learning. Our findings imply that it would be a positive educational development to design SEL curricula for systematic use across multiple grades, thus weaving these into the formal Chinese elementary school system.