While survey researchers have made efforts to avoid the occurrence of bias during each step of survey research, the roles and impact of field supervisors have not received enough attention. Field supervisors are the gatekeepers to ensure data quality since they are responsible for monitoring the conduct of interviewers. This paper examines the roles of field supervisors in the execution of survey questionnaires via face-to-face interview method by conducting qualitative interviews and observations with the field supervisors of Taiwan’s Election and Democratization Study, 2013 (TEDS 2013). It is found that the field supervisors play an important role which shapes the interviewers’ attitudes toward the standardized interview protocol. Furthermore, it is concluded that when a supervisor responsibly fulfills his or her duties, the quality of survey data is improved.