During the screening for the inhibitors of cellulose biosynthesis as herbicides, we discovered a Streptomyces sp. A6497 with a selective antifungal activity against cellulose containing Phytophthora parasitica, but not against cellulose lacking Candida albicans. The inhibitor was isolated and identified, using a series of chromatographies. Based on structure analyses with UV spectrophotometry, mass and various NMR, the inhibitor was identified as sangivamycin. The compound exhibited strong antifungal activities against P. parasitica (MIC; 3.125 $mu$g/ml). In particular, it showed strong herbicidal activities against various weeds in the greenhouse experiment. Taken together, these results suggest that sangivamycin is a useful lead compound for the development of new herbicides.