Employee theft has becoming a serious and challenging issue for all businesses, especially to hotel organizations where employees have easy access to cash, amenities, and other inventories and items. This research is based on the theory of planned behavior, equity theory, and reinforcement theory to study the factors affecting employee theft behavior as well as the moderating effect of the internal control system in the hotel industry in Vietnam. Data were collected through 312 questionnaire responses and 9 in-depth interviews. The results confirmed that personal characteristics, opportunities, unfair compensations, injustice, and unethical working environment do affect stealing behavior at work. Moreover, the internal control system is proved to moderate the attitude and intention to steal to stealing behavior relationships. These results will provide an essential reference for both academicians and professionals to conduct further empirical validation or develop appropriate internal programs to prevent hotel employee theft behaviors.