The purpose of this study is to investigate the effect of joint tenure between the board of directors and the CEO on investment in research and development among companies listed on the Tehran Stock Exchange. In this study, investment in research and development was considered as the dependent variable, and joint tenure between the board of directors and the CEO, board tenure, and female and male CEO tenure were considered as independent variables. The research method is applied and the method of collecting archival data. The statistical sample includes 95 companies during the period 2014 to 2019 (the total number of observations is 950 company-years). Hypotheses were tested using multivariate linear regression and the IViews software. The results of the study showed that joint tenure between the board of directors and the CEO has a significant effect on investment in research and development, and also that board of directors tenure has a significant effect on investment in research and development, but that the tenure of a female and male CEO does not have a significant effect on investment in research and development.