Corporate Social Responsibility(CSR) activities are increasing, but still have not reached a definitive conclusion as to the impact of CSR activities on financial performance. Prior studies have explained the relationship between CSR activities and financial performance through stakeholder theory, but discussions on internal stakeholders such as employees are limited compared to external stakeholders. Also, there is a limitation that related studies analyze internal stakeholder performance as a dependent variable and cannot explain whether actual CSR activities lead to financial performance. In this context, this study analyzed the relationship between CSR activities and job satisfaction of employees who are internal stakeholders, and the role of the firm size to moderate these relationships. In addition, it was verified whether employee job satisfaction mediates the relationship between CSR activities and corporate financial performance. For empirical analysis, we collected KEJI scores from the Korea Economic Justice Institute and job satisfaction scores from Job Planet for listed companies in Korea. Finally, 260 year-company data that can utilize all the data were analyzed using the Hekman two-stage model. As a result of analysis, it was found that the job satisfaction of employees positively mediates the relationship between CSR activities and financial performance. In addition, the effect of CSR activities on job satisfaction was found to decrease as the size of the company increased.