Since business failure often occurs due to employees’ unethical behaviors, firms make a substantial effort to develop ‘ethical’ culture by monitoring and improving employee’s ethics. Their elaborations not only drive the employee’s ethical conducts, but also can improve the employee’s work attitudes and behaviors, which may result in the improvement of the employee’s job performance. However, there is a lack of insights on whether enhancing the employee’s ethics improves individual job performance. The current research addresses this important question. We further examine the underlying mechanisms on how employee’s work ethics influences his/her own job performance. We propose that enhanced felt responsibility and relational coordination by an improvement of the employee’s work ethics increase the job performance. We then hypothesize that the mediation effects will be moderated by job level. Using a panel data of 1,669 employees working in a large IT service corporation, we empirically find that the employee’s work ethics is positively related to his/her job performance even controlling the past job performance. We also find the partial mediation effects of felt responsibility and relational coordination on the relationship between employee’s work ethics and job performance, and that the mediation effect by felt responsibility is moderated by employee’s job level. With the findings, we provide several important and interesting implications to the business ethics literature and business practitioners, especially, in the firm’s human resource management.