Using panel data on corporate social responsibility (CSR) matched with corporate proxy statement data for a large and representative sample of 1,492 publicly traded firms in Japan over 2006–2014, we provide fixed effect estimates on the positive and significant effects on gender diversity of CSR. Such effects are, however, felt only after two to three years. The CSR effects are larger and more significant for firms that adhere more closely to the participatory Japanese management system. Our findings are robust to the inclusion of controls capturing the mediating effects of various work–life balance practices, pointing to the direct impact of CSR on gender diversity.