This study aims to examine the moderating effect of participation in informal science activities on the associations among students' awareness of environmental issues and their attitudes toward science and epistemological beliefs. The data set included 9841 15-year-old students from four Chinese provinces (Beijing, Shanghai, Jiangsu, and Guangdong) who took part in the Programme for International Student Assessment (PISA) in 2015. Correlation analysis showed that there was a significant positive correlation between awareness of environmental issues and students' science self-efficacy, interest in science, enjoyment of science, and science epistemological beliefs. Multiple regression analysis further revealed that informal science activities had no moderating effect on the relationship between awareness of environmental issues and interest in science and science epistemological beliefs, but played a moderating effect on the relationship between awareness of environmental issues and enjoyment of science and science self-efficacy. This study revealed the benefits of awareness of environmental issues, informal science activities, and their interaction in science learning and provided insights in implementation of the results in science teaching.