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ABSTRACT Considering the major impact which changes in the real exchange rate and crude oil prices have on various sectors of Iran's economy and the importance of the financial markets role in economic growth and development, this paper aimed to investigate the effects of the changes in real exchange rate and crude oil prices on Tehran stock exchange using the Markov-Switching's nonlinear models. To this end, daily data which belonged to the following periods were used: 20:03: 2005 - 13:10:2010 The result of the estimations obtained through the Markov Switching Models indicated that MSIAH model with two regimes out of the various MS model are the most suitable ones. The result of the research showed that the changes in the exogenous variable of real exchange rate and the crude oil price have lagging positive effect on the Stock Exchange Index. Moreover, the effects of these changes with two lagging time intervals are significant and negative. The practical implications of these findings could be beneficial to the investors and policy makers who need to be aware of the exact nature of the effects which changes in the exchange rate and crude oil prices have on the stock exchange index.