Corporate Social Responsibility (CSR) concept is closely related to the notion of sustainable development, and the outcome of the sustainable development approach is specific consideration to disclosure and reporting of CSR. One factor that is less considered in the Iranian economic environment and research is the competitive nature of the product market in today's highly competitive and sensitive environment. So, the main aim of this paper is to investigate the moderating effect of competition in the product market on the debts ratio and the CSR relation among companies listed on the Tehran Stock Exchange. The independent variable in this study is CSR, and the dependent variable is the debts ratio. In order to investigate this issue, the research sample was determined using the systematic elimination method, and 97 companies were selected for seven years from 2012 to 2018. Multivariate regression was used to analyze the data and test the hypothesis. For this purpose, the output-oriented BCC model has been used to measure companies' CSR, and the Lerner index has been used to represent competition in the product market. The results show that high competition in the product market moderates the relationship between CSR and debts ratio. In other words, when competition in the product market is high, Firms adopt lower debt ratios by fulfilling their social responsibilities. The investigation of the moderating effect of the competition is the distinguishing feature of our research compared to other studies. Therefore, players of industry, business, creditors, and investors should pay attention to the intensity of competition in the market.
