Recently, customer aggression occurring in the service organization has become a social issue. “The customer is always right” is a omnipresent organizational mantra, followed closely by “service with a smile”(Rafaeli and Sutton, 1987). In fact that in a consumer-centered economy it is impossible to ignore the effects of customer satisfaction on organizational performance. However, the core problem of these formulas is a power imbalance between customers and employees, that may lead customer to take advantage of employees. Indeed, many studies are reporting the dark side of customer-employee transactions, where service providers are targets of customer aggression. Such experiences can cause organizational as well as personal costs. For instance, customer aggression has been found to be a predictor of job burnout, absence, turnover intension, and emotional exhaustion (Ben-Zur and Yagil, 2005; Glomb, 2002; Grandey et al., 2004; Harris and Reynolds, 2003). Moreover, customer aggression has been found to predict a decrease in job performance, an increase in employee withdrawal behavior(공혜원, 김효선, 2014; Bedi and Schat, 2007; Glomb, 2002). It is revealed that psychological ownership can influence job attitude and behavior of employees (Pierce et al., 2001). Although It has been reported that customer aggression has negative effect on employees and organizations, but little attention has been given to the study on the relationship among customer aggression, deviant behavior, and psychological ownership is unknown. Especially, very few attempts have been made at the moderating effect of psychological ownership. Therefore, the purpose of this study is to examine the main effect of customer aggression and psychological ownership on deviant behavior(Organizational deviance, Interpersonal deviance) and the moderating effect of psychological ownership on the relationship between customer aggression and deviant behavior. It was hypothesized, in this study, that 1) Customer aggression is positively related to organizational deviance and interpersonal deviance. 2) Psychological ownership is negatively related to organizational deviance and interpersonal deviance. 3) The positive relationship between customer aggression and deviant behavior(organizational and interpersonal deviance) is stronger for those who had lower psychological ownership. To test these relationships empirically, we collected data from 394 workers engaging in financial services, including those who work in the banking sector and customer call center of banks. A SEM (structural equation model) was used for the test of hypotheses. Findings are as follows. First, it is confirmed that customer aggression increases both organizational deviance and interpersonal deviance. Second, those who had higher psychological ownership were less likely to show organizational deviance. However, the relationship between psychological ownership and interpersonal deviance is not significant. Lastly, it turned out that the moderating effect of psychological ownership is significant only in the relationship between customer aggression and interpersonal deviance. For instance, an employee with a high level of psychological ownership increases interpersonal deviant behavior for colleagues in the case where customer aggression increases. The findings of this study suggest that organizations should no longer turn a blind eye to inappropriate customer behavior under the pretext of serving customers. Rather, organizations should prepare a selective customer response policy. Also, organization managers should keep in mind that psychological ownership is a “double-edged sword” that has both positive and negative effects on the organization, and take precautions in the proposal of human resource management solutions in the future.