The foraminiferal content of the Gurpi Formation at the type section in Anbar Sefid Valley NE of Lali city in Masjed Soliman was studied. The recorded foraminifera indicate an age of Late Paleocene for the upper boundary of the formation that turns to purple sandy and silty shales at the base of the Pabdeh Formation. The K/T boundary lies 57m below the purple key layers. The Study of the foraminifera at the K/T boundary demonstrates that the specialist polytaxic species with large size and complex morphology (such as pseudotextularids, rugoglobigerinids and globotruncanids) which were sensitive to changes in environmental condition disappeared ,while generalist oligotaxic species with small size, simple morphology and fine shells (such as hedbergellids and heterohelicids) became domi-nant. As the changes in fauna's composition are usually raised from ecological factors, thus the changes in the most important ecological factors such as salinity, temperature, Oxygen, PH, sub-surface currents and nutrient supply have been evaluated to interpret the changes in faunal composition. Definite decreases in temperature, salinity, Oxygen amount and pH and increase in sea current and nutrient amount have been concluded as the most important factors effecting faunal changes across the K/T boundary. These changes in ecological factors might have been results of an increase in upwelling currents generated in Early Paleocene preceded by a regression at the end of Cretaceous.