Nine Trichoderma isolates were isolated from agricultural soil samples collected from Fayoum governorates, Egypt. Based on morphological and cultural characteristics, the Trichoderma isolates was identified as Trichoderma harzianum.  All the nine Trichoderma isolates showed positive test for cellulose production. The percentage inhibitory effect of all the nine Trichoderma isolates against growth of Rhizoctonia solani was calculated and ranged from 57.6% to 64.9%. The isolate FUGT3 was showed the greatest antagonistic effect to the R. solani (64.9%) whereas isolate FUGT4 showed lowest antagonistic against R. solani.  Cellulase producing from Trichoderm isolates was determined spectrophotometry and isolates FUGT3 showed highest CMCase activities (0.32 IU/ml). Molecular phylogenetic analyses indicate that the isolates FUGT3 was closely related to T. harzianum with accession number OL953189. The selected strain FUGT3 was subjected to mutation using UV-radiation and 12 mutants were obtained. These mutants were tested for their cellulase productivity compared to their wild type and the results showed that, the wild strain exhibited the cellulase activity 0.1 IU/ml on carboxy methyl cellulose (1.0%). Upon mutation by UV exposure the Trichoderma mutants produced cellulase 1 IU/ml. The mutants from UV were selected and ISSR analysis of genomic DNA was performed to detect genetic diversity of these mutants with the wild type by using 6 primers. The pattern attained by primers illustrated that all the mutant genotypes depicted entirely different patterns of DNA amplification in comparison to the wild type strain. The obtained mutant Trichoderma strain had high potential to overproduce the cellulase.