The paper deals with the floral diversity and species richness in the Valley of Flowers National Park, located in Chamoli district of Western Himalaya.Extensive systematic survey was conducted covering various eco-climatic zones, landscape units and seasons during 1993-1997. A total of 520 species of vascular plant, distributed over 72 families and 248 genera, were found within the National Park. Fifty nine species were recorded for the first time from the Valley of Flowers, of which 4 species are new records for the Uttar Pradesh Himalaya.Asteraceae was the largest family followed by Rosaceae and Ranunculaceae in the Park area. The diversity and richness of plant species decrease with the increase in altitude from sub-alpine to higher alpine zone. The results of floral inventory and systematic study of floral diversity have been discussed.