Oil revenues make up the major part of revenues of the oil exporting countries. So, the fluctuation of oil price is very important for these countries. This study investigates the asymmetric effects of oil shocks on output in Iran over the period of 1369:1-1386:6 using the Markov switching approach. The results suggest that the effects of oil shocks on output are separable into two regimes. In addition, the results also show that the effect of oil shocks over the recessions is significantly higher than that over the booms. In other words, the impacts of oil shocks on output in the Iranian economy over the booms and recessions are asymmetric.