The paper provides annotated Checklist of Bulgarian thermal algae mentioned in the publications on thermo-mineral springs, baths and their effluents and updated according to the last taxonomic considerations. The list contains data on 35 thermal systems and totally 206 taxa from five algal divisions (phyla): Cyanoprokaryota (82), Rhodophyta (4), Ochrophyta (44: 3 - Tribophyceae, 40 - Bacillariophyceae), Chlorophyta (32) and Streptophyta (44). Among them 21 species are of conservation importance according to the Red Lists of Bulgarian macroalgae and microalgae, and of the Red Data Book of R Bulgaria as well. According to their threatened status they are spread in the following groups: Critically Endangered (1), Endangered (4), Vulnerable (6), Near Threatened (5) and Data Deficient (5). On the background of the increased pace of habitat losses due to capturing of the springs, construction of new modern SPA centers with permanent cleaning of the algae, or usage of springs for heating purposes or as laundries, this Checklist can serve as a basic archive for future investigations of this important ecological group of extremophilic algae.