Making capital and investment is the main driving forces of economic development. Based on the investment sensitivity to the changes of some of macro-economic variables and risk and uncertainty, the present study evaluated the effective factors on investment in private sector in Iran during 1980-2007. At first, the uncertainty variables of real informal exchange rate, nominal interest rate and inflation rate were calculated by GARCH model. Then, by ARDL model, the effect of calculated uncertainty indices besides the main values of the variables and some of the other control variables on investment in private sector in Iran was investigated. The estimation results showed the negative uncertainty effect of the real exchange rate, inflation rate and nominal interest rate on investment in private sector in short-term and long-term. Also, the gross domestic production and inflation rate had significant and positive and negative effect, respectively on investment in private sector in Iran. In this model, there was no relationship between the size of civil expenditures of the government and real exchange rate with the private sector investment in our country. The error correction term coefficient showed that moderation to balance is done during more than 3 years. Manuscript profile