<p>Career decision-making self-efficacy (CDMSE) plays an important role in young people’s identity development and career choices. However, the underlying mechanisms may differ depending on the social context of each country. We examined individual (self-esteem and career preparation behavior) and environmental (support from others and career education) factors related to CDMSE among university students in Japan and China. Data were collected from 110 students in Japan (June–August 2022) and 165 students in China (November 2022), and structural equation modeling based on a multi-group analysis was conducted. In both countries, maternal emotional support enhanced CDMSE through students’ career preparation behavior and self-esteem. Additionally, emotional support from peers was positively related to self-esteem, whereas informational support from peers was negatively related to it. These findings suggest that emotional support from mothers and peers may be universally important for career development, whereas the negative effects of informational support from peers may reflect the influence of highly competitive social environments. Cross-national differences were also observed. In Japan, career education at universities promoted career preparation behavior, which in turn enhanced CDMSE, whereas this effect was not observed in China. This finding suggests that well-developed career support systems in Japanese universities play an important role for students as they prepare to enter society.</p>