Palynological investigation on 132 samples from the 428m thick outcrop section of Late Paleocene to Early Oligocene of the Pabdeh Formation in southwestern Iran yielded 55 species of dinoflagellate cysts and allowed establishment of seven biozones. Quantity of marine palynomorph elements indicate an open marine environment at that time interval but, a slight increase in number of spore and pollen grains in some samples indicate suitable conditions for forest development as a consequence of increase in climate humidity. The species are common in various latitudes and most of them are cosmopolitan. Thermal maturity index measurement indicates oil prone nature for majority of the samples.Keyword: Pabdeh Formation, Dinoflagellate cysts, Paleogene, Palynostratigraphy, Thermal maturity