The purpose of this study is to investigate the determinants of stock investors’ intention towards using mobile stock trading. Based on a modified UTAUT (unified theory of acceptance and use of technology) with risk perceptions, a comprehensive research model was proposed. An empirical survey with a valid sample of 329 stock investors was conducted in Taiwan to test the research model. The analysis results of PLS reveal three positive determinants (i.e., performance expectancy, effort expectancy, and social influence) and three negative determinants (i.e., security risk, economic risk, and functional risk) that significantly influence stock investors’ behavioral intention to use mobile stock trading. Furthermore, the results of moderating effect analysis indicate that gender differences moderate the effects of social influence on behavioral intention to use mobile stock trading, while age differences moderate the impact of effort expectancy on mobile stock trading use intention. This implies that to facilitate the intention to use mobile stock trading, securities firms need to consider stock investors’ technological perceptions and risk perceptions of this type of trading. The findings of this study not only have important implications for m-commerce research, but also provide insights for securities firms and developers of mobile stock trading systems.