Effects of the inoculum size of testing organism and pH of the plate and the concentration of agar were investigated for the selection of high kasugamycin producing mutants of Streptomyces kasugaensis ATCC 15114. For the detection of high kasugamycin-producing mutants, both concentrations of agar and test organism were optimized at the concentrations of 2% and 0.35 (A$_{550}$), respectively. The pH 7 was optimum for both growing the testing organism, Pseudomonas fluorescens IFO 12180, and for obtaining more promising mutant strains of S. kasugaensis. Under these conditions, mutants had been isolated which, tested later in liquid cultures, gave higher kasugamycin yields than that of the parent strain.