Endo-1, 4-β-glucanase is one of three cellulolytic enzymes in a triplet catalytic system that are required for extracellular cellulose hydrolysis. Thermostable endo-1, 4-β-glucanase is important and is included in a considerable portion of industrial enzymes. Hot springs are extreme niches which are important sources of the bacteria producing thermostable enzymes. Accordingly in this study, sampling was performed from four hot springs in the north and northwest of Iran and the screening and identification of acid-stable and thermostable of endo 1, 4-β-glucanase producing bacteria was investigated. Endo1, 4-β-glucanase activity of these isolated strains were determined by qualitative Congo-Red staining as well as quantitative Carboxymethyl cellulose/Dinitrosalicylic acid methods as indicators of cellulase production. Three isolates out of twelve initially selected bacteria showed noticeable endo 1, 4-β-glucanase activity, including Paenibacillus sp. ASh 4, Bacillus sp. AGh1 and Bacillus sp. AG2 with 90 %, 77 % and 45 % residual activity at pH 4, 60 º C after three hours. Molecular identification of the bacteria was carried out using 16 S rDNA partial sequencing, in which two isolates were shown to belong to Bacillus sp. and one to Paenibacillus sp. . The results showed that the isolated acido-thermotolerant Bacillus spp. and Paenibacillus sp. had the capability to produce suitable acid-stable and thermostable endoglucanase. These isolates may also be considered as candidates for the production of other thermostable metabolites with additional biotechnological applications.