This research was carried out to screen and characterize thermophilic bacteria that have the ability to produce cellulase enzyme. Bacterial strains were isolated from the sediment samples collected from Ras-Sedr's hot spring located in Ras-Sedr, Egypt. For cellulolytic activity testing, Carboxymethylcellulose (CMC) agar was used as growth medium. Seven bacterial isolates showed variable zones of CMC clearance. Evaluation of cellulase enzyme thermal activity was carried out at varying temperatures from 35°C to 85°C and the impact of pH on cellulase activity was evaluated at different pH levels of 5-9. Molecular identification for the isolates also conducted based on 16S rRNA gene sequencing. At 55°C and pH 7, all the seven bacterial isolates showed their optimum growth conditions. Strains were gram positive, have rod shape cells, spore forming and motile with the ability to produce thermostable cellulase. The results of the phylogenetic analysis reveal a high degree of sequence similarity between the isolated bacteria involved in this research and Geobacillus sp. These thermophiles have the ability to produce useful thermostable cellulase enzyme of industrial significance, which in turn indicates that Ras-Sedr's hot spring considered a prospective source of economically significant microorganisms which needs more studies through further researches.