Hand hygiene is one of the most important factors for decreasing the healthcareassociated infections (HAIs). The aim of this study was to evaluate the role and efficacy of the mystic surveyor in the promotion of hand hygiene program in a medical center. In 2008, the rate of hand hygiene compliance (HHC) was low. The infection control committee of the hospital set up and trained the mystic surveyor team to perform surveillance and improve the rate of HHC every month. The mystic surveyor improved the surveillance of hand hygiene and prevented the Hawthorne effect in the hand hygiene surveillance. The HHC rates increased from 63.9% in 2008 to 89.6% in 2012, and the HAI rates decreased at the same time points. The role of the mystic surveyor is important in the hand hygiene program.