In this study the relationship between the competitive structure of products and conditional accounting conservatism in Tehran Stock Exchange has been examined. Data of the sample companies for a period 1380-1388 is collected. In order to estimate conditional accounting conservatism, Basu model (1997) is used. Similar to Folsoms model (2009), product market competition constructs are added to Basu model and the main model of research is obtained. Several criteria is applied to measure competition because, competition is a multi-dimensional case. The most important ones include: the product substitutability, the volume of demand, entry barriers, concentration ratio and the number of companies. The relationship between competitive structures and conditional conservatism in general and specific hypotheses are set. A five-fold aspect of the relationship between competition and conditional conservatism in five specific hypotheses is investigated. Using these dimensions, a combination of variables is obtained and as general hypotheses, the relationship between competitive and conditional accounting conservatism is investigated. Testing of specific hypotheses suggests that contrary to expectations, there is significant and inverse relationship between product substitutability, and conditional conservatism. The relationship between the volume of demand and the number of member companies, industries with conditional conservatism as expected, is positive and significant. Also, the relationship between entry barriers and the desire for conditional conservatism, and the reverse is significant. Finally, the relationship between the concentration ratio and conditional conservatism as it was expected is inverse, but it is poorly observed. The test of overall hypothesis shows that there is a direct and significant relationship between structures of competitive products and conditional accounting conservatism in financial reporting.