Palaeobotanical study on the plant fossils (petrified woods and a leaf and) from Siwalik (Miocene) sediments of Kalagarh area, Uttarakhand has revealed the occurrence of 40 species belonging to 26 genera of 14 angiospermous families. The family Dipterocarpaceae (Sal family) represented by 12 species is the most dominant family in this Kalagarh fossil assemblage followed by Fabaceae (9 species). The evergreen elements dominate the fossil flora in Kalagarh area during Miocene in contrast to mixed deciduous elements at present. The predominance of evergreen elements in the Siwalik fossil assemblage indicates the prevalence of tropical warm humid climate with plenty of rainfall during the deposition of Siwalik sediments. The analysis of present day distribution of all the species recovered from the Siwalik of Kalagarh area shows that they are mostly known to occur in South East Asia, North-East India and Indo –Malayan region wherever favorable climatic conditions exist. Only about 17% species of the total assemblage are found to grow presently in the Himalayan foothills and the remaining species are locally extinct which suggests a change in the climatic condition after Miocene. The floral assemblage also indicates that tropical evergreen to moist deciduous plants were flourishing in Kalagarh and nearby area during Miocene in contrast to the mixed deciduous plants at present. The local extinction of most of the comparable extant species of the fossils indicates that a change in the climate must have taken place since Miocene most probably due to uplift of Himalaya. The Coexistence Approach (CoA) for palaeoclimate estimation suggests that the Kalagarh area was enjoyed with tropical climate during Upper Miocene having Mean Annual Precipitation (MAP) 2100-3100 mm and Mean Annual Temperature (MAT) 21.5-31.5°C). The presence of diffuse porous condition in all the fossil woods along with medium to large vessels and abundant parenchyma further suggest the prevalence of tropical humid climate in the region during Miocene.