Abstract: Biological control of causal pathogen (Macrophomina phaseolina) was investigated by four strains of Streptomyces. Dual culture and cellophane overlay technique were used in vitro assay. All antagonist - host combination were carried out in 4 replicates. Colony area was recorded daily, compared with controls and percentage of growth inhibition was calculated. Glasshouse studies were performed to test the ability of Streptomyces strains incorporated to the soil as a rate of 10g kg-1 potting mix. In other experiment seeds of melon were soaked in Streptomyces suspension and planted in infected soil with pathogen. Streptomyces strains significantly inhibited mycelial growth of Macrophomina phaseolina in dual culture. Streptomyces strains, STL, A20, and A15 inhibited the growth of pathogen by 88.16 to 89.3% and mycelial growth of M. phseolina was reduced 69.99% by Streptomyces strain A22. Cell free metabolites produced by 4 strains of Streptomyces reduced colony area by 80.14-99.66%. The results of glasshouse experiment indicated that when soil of pots inoculated with pathogen + Streptomyces or Streptomyces alone, percentage of healthy plants were significantly greater than in those of pathogen control (p<0.05). Similar results were obtained in seed treatment test.