Synopsis The present work on the Algal Flora of Dehradun district, Uttaranchal has been carried out to assess and inventorise the algal diversity in an area encompassing varied ecoclimatic zones. The flora has a rich assemblage of many interesting algae. Unfortunately, the area being a tourist spot, is subjected to severe anthropogenic activities which are causing extreme stress conditions on the algal habitats. The flora deals with taxonomic treatment of 321 taxa, of which, 150 belonging to chlorophyceae, 81 to Myxophyceae, 53 to Bacillariophyceae, 18 to Euglenineae, 5 to Xanthophyceae and 2 each to Dinophyceae and Rhodophyceae, each with original citation, description, phenology, habitat, association, field numbers, etc. Taxonomic keys and camera lucida drawings of all taxa have also been provided.