Kiyasar National Park is a mountainous region in Mazandaran province, Kiyasar district, 70 kilometers far from Sari city, with an area of approximately 9530 hectares. The altitude of the area ranges from 883 m to 2775 m in Shahdeg pick. This park is located in the central Alborz. The mean annual rainfall is 650 mm and the mean annual temperature is 12˚C. Based on classical methods of regional floristic studies, approximately 720 specimens were collected during 2007 through 2008. The total number of 378 identified plant species belonged to 321 genera and 73 families. The dicots with 320 species were the richest group, following by monocots with 49 species, gymnosperms with 4 species and pteridophytes with 5 species respectively. The largest families were Asteraceae (43 species), Lamiaceae (33 species), and the most diverse genera included Astragalus, Salvia and Stachys. There were 11 endemic species among the plants of the area. The life form of all plant species was determined via Raunkier,s method. Hemicryptophytes constituting 37% of the biological types were dominant, followed by therophytes and cryphtophytes with 31% and 16% respectively. The largest chorotype was Irano-Turanian, with 120 species.