BACKGROUND: Although nurses' workplace social capital for a healthy work environment has received considerable attention, few scales about nurses' workplace social capital are based on the attributes of clinical settings in Japan. This study aims to develop a Relational Workplace Social Capital Scale for Japanese Nurses (RWSCS-JN), which includes bonding, linking, and bridging social capital and assessing its reliability and validity. METHODS: We assessed its reliability and validity using questionnaire survey data collected from 309 nurses in the first survey and 105 nurses in the second survey in four hospitals in Japan. First, we determined the number of factors and items for the RWSCS-JN through the parallel and factor analyses after conducting the item analysis. Then, we confirmed the omega coefficients and intraclass correlation coefficients (ICC) of the RWSCS-JN. Finally, we examined the Pearson product-moment correlation coefficient between the RWSCS-JN score and other variables, including an existing measurement of workplace social capital, work engagement, and turnover intention. RESULTS: The newly developed RWSCS-JN contained 15 items, comprising three factors as follows: bonding social capital, linking social capital, and bridging social capital. The omega coefficient and the ICC of the RWSCS-JN were 0.90 and 0.85, respectively. The Pearson product-moment correlation coefficient between the RWSCS-JN and the existing scale of the workplace social capital was 0.88 (p < 0.01). Furthermore, the Pearson product-moment correlation coefficient between the RWSCS-JN and work engagement was 0.36 (p < 0.01) and that of the RWSCS-JN and turnover intention was - 0.40 (p < 0.01). CONCLUSIONS: This study suggests that the RWSCS-JN could be sufficiently useful for a healthy work environment in a clinical setting.