The impact of ENSO phase transition on the sea level pressure and precipitation in Iran Autumn during the period of 1950-2018 has been analyzed. The Oceanic Nino Index (ONI) was used to select ENSO events and also ENSO phase transition from El Nino to La Nina events (type 1) and vice versa (type 2). each case divided to four cases individually as following for type 1: Strong El Nino to Strong La Nina, strong El Nino to weak La Nina, weak El Nino to strong La Nina, weak El Nino to weak La Nina and also for type 2: strong La Nina to strong El Nino, Strong La Nina to weak El Nino, weak La Nina to strong El Nino and weak La Nina to weak El Nino. Monthly and climate mean precipitation and Sea Level Pressure (SLP) data were obtained from NCEP/NCAR reanalysis during 1950-2018. With these datasets, composites of means and anomalies of SLP and precipitation (lands only) in Iran Autumn were made based on cases of two types of ENSO phase transition. Finally, the student's t-test was used to compare the significance of the composites means in each grid point. Results reveal the weakening of the Iceland low and Azores high pressure in type 1 and reinforcement of both in type 2 with statistically significant of 99% confidence level. pressure anomaly values over Iran is normal or less than normal in event type 1 and less than normal in type 2 with statistically significant at 75% confidence level for north and east of country. The composite analysis of precipitation anomaly shows, during ENSO phase transition type 1 most regions of Iran have experienced low precipitation while in type 2 in the nearly all region precipitation is more than normal and also statistically significant at 75% confidence level or higher, spatially in north half for both.