A suitable competitive strategy can lead to a competitive advantage, and to achieve a competitive advantage, a competitive strategy must be formulated. Choosing the right competitive strategy is a complicated and even risky task. Decision making in the field of strategies commits the organization to produce certain products, operate in certain markets, and use known resources and technologies for a long period of time. Based on this, organizations try to survive and grow in the dynamic field of competition by formulating appropriate strategies, hence the purpose of this research is to investigate whether competition in the product market has an effect on the commercial defensive strategy of companies admitted to the stock exchange. Does Tehran have an effect? which was done using 120 companies admitted to the Tehran Stock Exchange between 2014 and 2014 and with a sample of 120 companies and also using multivariable linear regression. The results of the research findings showed that competition in the product market has a significant effect on the commercial defensive strategy of companies listed on the Tehran Stock Exchange.