The objective of this study is to explore the effects of catechin-treated face masks on influenza prevention. We conducted a randomized controlled study in Japan. Participants included workers in a nursing home, a rehabilitation facility, and a hospital. Participants were randomly allocated into the catechin-treated (epigallocatechin gallate-treated) or non-treated face mask groups for 60 days from January to March, 2016. Incidence of laboratory-confirmed influenza infection was measured and compared between groups using Fisher's exact test. Multivariate analysis was performed to calculate adjusted odds ratios (OR) and associated 95% confidence intervals (CI). After the recruitment of participants, 234 participants were eligible for the study (catechin group, n=118; control group, n=116). Six participants in the full analysis set contracted influenza (catechin: 3.39%; 95% CI: 0.95-5.50%; control: 1.72%; 95% CI: 0.21-6.09%), and the incidence between the groups did not differ significantly (P=0.68). Multivariate analysis showed a similar trend (adjusted OR: 2.35; 95% CI: 0.40-13.72; P=0.34). Our results suggest that the use of catechin-treated face masks does not reduce influenza incidence compared with standard masks. Several limitations to the study, such as infection rates and the selected population may be responsible. Future studies will need to resolve these limitations to accurately evaluate these effects.