Abstarct: In this research, the effect of market structure, price and customs tariff on market share of selected products of Iran Khodro and Saipa have been investigated using dynamic combination data method (GMM method). The realm of this research period is 2004-2014. Market share has been used as a dependent variable and market structure, price and tariff as independent variable. The results of model estimation show that the degree of concentration with the market share of selected products of Iran Khodro and Saipa have a significant and positive relationship. Also, prices, production and sales are negative with the market share of selected products, and the customs tariff variable has no significant relationship. Hence, the most important policy recommendation of the study is to eliminate customs tariffs as a coherent program, as this rate has eliminated the competition of domestic automobile firms with other foreign manufacturers and one of the factors that does not pay much attention to the quality of domestic automobiles. Also, according to the results of this study, it is recommended that government support be phased out and that the market returns from a monopoly to a competitive state, in which case car prices will be more realistic.