The present study investigates the effect of goodwill on the financial performance of companies listed on the Tehran Stock Exchange. Investors need financial information to make their investments so they can make the right decision. Financial statements play a major role in describing the financial condition and financial performance of companies. Recognizing, measuring and disclosing intangible assets in financial statements is one of the major challenges. Some intangible assets, including goodwill and other identifiable intangible assets, are recorded and reported in business combinations and acquisitions of corporate stocks. Proper analysis of the factors affecting the financial performance of companies can help investors to make optimal decisions. In this study, to calculate goodwill from its book value in the main financial statements of companies and to calculate the financial performance of companies, the criterion of return on equity has been used. This research is a descriptive-correlational study based on the analysis of composite data. 80 companies listed on the stock exchange during the period 1300-1400 have been selected as a sample. Based on the test results, goodwill has a positive and significant effect on companies' financial performance.