PurposeThis study aims to determine the effect of board gender diversity on cyber security disclosure (CSD) in the banking sector of Indonesia as a developing country that adheres to a two-tier system.Design/methodology/approachThis study uses a panel data of 47 banks listed on the Indonesia Stock Exchange from 2014 to 2021. The board gender diversity is measured by three proxies, the proportion of women on the board, BLAU Index value and the critical mass of women. The authors used generalized method of moments estimation to eliminate the simultaneous equation bias.FindingsThe results show that the women board of commissioners increases CSD, and the women of board of directors/top management team were significantly negative for CSD.Research limitations/implicationsFirst, this research was only conducted in the banking sector. The results cannot be generalized to non-financial companies. Second, there is no measurement of the quality of the board from the level of education, experience, expertise and other characteristics of diversity such as age, nationality and religion.Practical implicationsThe study has revealed the need for the government’s role in providing oversight of the presence of women on the board so that banks fully comply with Indonesia Financial Services Authority regulations. Banks should also actively launch policies regarding the presence of women on the board to give a positive effect to stakeholders that women play an important role in decision making. Banks must also adjust the composition of female commissioners with a threshold of two people to maximize their function as supervisors.Originality/valueThis is the first research conducted on the banking sector in Indonesia as a developing country that adheres to a two-tier system. The results of this study provide evidence that patriarchal culture is still dominant in Indonesia.