Erwnia carotovora is known to cause bacterial stalk rot of plants. Culture filtrates of 159 strains of Streptomyces species freshly isolated in this laboratory have been screened for inhibitory activity against E. carotovora using the paper disc-agar plate method on nutrient agar. Twenty-six Streptomyces strains showed inhibitory zones against E. carotovora, but not against other gram-positive and negative bacteria. While 3 strains showed clear inhibitory zones against E. carotovora as well as against other gram-positive and negative bacteria. One of the above 26 Streptomyces strains, designated as Streptomyces H 359 NSY 6, was studied to isolate the antibiotic which was found to be maltotetraose. Until now, maltotetraose has not been reported as an antibiotic of Streptomyces origin. Cultivation, isolation and purification of the antibiotic and its identity with maltotetraose will be described in this paper.