This study explores speaking self-efficacy for university EFL students in Japan. The primary objectives of the study were to analyse the growth of self-efficacy over time, potential differences between male and female students, and the relationship between self-efficacy, casual attribution, and outcome satisfaction. While several studies have shown a correlation between self-efficacy and achievement in language learning (Raoofi et al. 2012), there are few studies that have focused specifically on the domain of speaking. 58 first- and second-year Japanese students filled out a series of three questionnaires in conjunction with a standardised speaking test given at two points during a 15-week semester. ANOVA results indicated a significant growth in self-efficacy for the speaking test, and that male students reported significantly higher self-efficacy than the female students. Furthermore, correlational analysis showed a moderate relationship between self-efficacy and stability attributions on the final speaking test, as well as a weak but significant negative relationship between self-efficacy and outcome satisfaction. These results highlight the need for more fine-grained analysis of self-efficacy in language learning to gain clearer insight into how it develops over time, the psychological constructs that interact with it, and the potential impact on task valuation and outcome expectancy.