In response to growing concerns about adolescents' low expectations for science-related careers, this study explores the mechanisms of the ternary associations among science learning experiences, science-related attitudes and beliefs, and science-related career expectations, involving a sample of 9841 15-year-old students from four Chinese provinces (Beijing, Shanghai, Jiangsu, and Guangdong) who took part in the sixth cycle of the Programme for International Student Assessment (PISA). The results of the path analysis reveal that: (1) both formal and informal learning experiences had positive relationships with science-related attitudes and beliefs; (2) enjoyment of science, science self-efficacy, science outcome expectations, and epistemological beliefs about science had positive effects on career expectations; (3) inquiry-based learning experiences were negatively associated with career expectations, although the direct association was suppressed by enjoyment of science, science self-efficacy, and science outcome expectations; (4) teacher-directed science learning experiences had a positive impact on career expectations, fully mediated by enjoyment of science, epistemological beliefs about science, and science outcome expectations; and (5) all four science-related attitudes and beliefs played full mediating roles in the relationship between informal science learning experiences and career expectations.