In recent years, corporate social responsibility (CSR) has expanded to include broader issues such as the environment, human rights, and anti-corruption. Companies can fulfill part of their accountability to society by disclosing information beyond financial data, thus providing a basis for better decision-making for stakeholders. The efficiency of a market relies on the presence of a transparent and public flow of information, and the success of an efficient market hinges on its ability to continuously reflect new information in the prices of securities. Accordingly, this research aims to investigate the relationship between CSR disclosure and the market efficiency of the listed companies on the Tehran Stock Exchange. To this end, 450 firm-year observations during the years 2016-2020 were selected through systematic elimination sampling. The level of CSR disclosure was measured using the board of directors' reports and the annual financial statements of the companies. The CSR ranking index was assessed through content analysis of these reports. Capital market efficiency was measured using the Olson residual income model, which indicates semi-strong market efficiency. The hypotheses were tested using panel data methodology and Eviews 10 software. The test results show that not all information is reflected in stock prices, which might be attributed to the inefficiency of the Iranian capital market. Therefore, CSR disclosure does not significantly impact the stock market efficiency, and the hypothesis of stock market efficiency in Iran cannot be confirmed.