Cellulases have been considered as effective biocatalysts because of their diversity of applications. A total of 165 cellulase producing Streptomyces isolates were recovered from Egyptian soil samples via cultivation on carboxymethyl cellulose agar medium. The results of screening by Congo red method showed that the tested isolates revealed different levels of cellulase activity. The isolates showed high level of cellulase production (clear zones ˃ 25 mm, n= 15) were submitted for quantitative evaluation of their cellulase productivities by using dinitrosalicylic acid assay. Cellulase production of these selected isolates ranged from 146.9 to 650.5 U/L. The highest cellulase-producing isolate (S11-6) was identified at the molecular level using 16S rRNA gene sequencing. The sequence homology analysis proved its close proximity and relatedness to Streptomyces coelicoflavus strain NBRC 15399. Production improvement of cellulase was carried out by genetic manipulation using a dose of 4 Kilogray (KGy) of gamma radiation. M1 mutant showed 1.31 fold increment in cellulase production as compared to the wild type strain of S. coelicoflavus.