ObjectivesIn this study, we conducted a cluster randomized control trial to verify the effectiveness of a treatment work balance support (TWBS) program promoted by occupational health nurses (OHNs) in small and medium‐sized enterprises (SMEs) using a web meeting system.MethodsWe analyzed data from 64 managers (32 each in the control and intervention groups) and 541 workers (246 and 295 in the control and intervention groups, respectively) from 22 SMEs (11 in each group) with less than 200 workers. The TWBS program comprised online consultations for managers and seminars for workers by an OHN. TWBS leaflets were distributed among both groups. The “Recognition and Attitude Scale toward TWBS” was administered and workplace climate, psychological safety (PS), and work engagement (WE) scores were measured at baseline and endpoint. The increase in scores of each group was analyzed using a linear mixed‐effects model.ResultsIncreases in managers' scores on all three recognition and attitude subscales were significantly greater in the intervention than in the control group (P = .048, .003, and .032, respectively). Workers' score increases were significantly higher on two subscales—recognition of workplace initiatives and understanding of professionals' roles—in the intervention than in the control group (P = .043 and .001, respectively). There was no difference between the two groups in the amount of increase in PS and WE, as perceived by managers and workers.ConclusionsThe TWBS program by OHNs increased recognition and attitude among SME managers and workers, indicating the usability of promoting TWBS in SMEs.