Cucumber is one of Egypt's most popular vegetables, although it is sensitive to a number of plant diseases. The current study aimed to develop superior Streptomyces bacteria for improved antagonistic to fungi using mutagenic agents. Two Streptomyces isolates were isolated from Egyptian soil and identified by biochemical methods according to Bergey's Manual and partial 16S rRNA sequencing. These isolates were phenotypically identified as Streptomycetes genera. Mutation experiment by using chemical ethyl methanesulfonate (EMS) mutation methods. Through mutagenesis by (EMS) out of 10 obtained mutants. The mutants of Streptomyces isolates gave height antagonism of cucumber plant fungi Fusarium, Pythium and Rhizoctonia on the plates selected and applied in pots experiments growing cucumber. Streptomyces isolates and their mutants gave high inhibition percentage for the three (the studied) pathogenic fungi compared with the control. In soil infested with Pythium deberianum and Rhizoctonia solani treatments with mutants 6, 7 and Topsin-M70 fungicide increased the percentage of survival plants by up to 85% compared with the control (40%). While the mutants 5. With Fusarium oxysporium 75 %.  survival plants. While mutant 4 with Rhizoctonia solani and 2 and 9 Fusarium oxysporium had the lowest effect on increasing cucumber survival (55%) and mutant 2,8 on Pythium deberianum gave 60% compared with other treatments and control. This finding suggests that Streptomyces could be useful in protecting plants such as cucumbers from fungi and reducing environmental contamination with herbicides.