Bacterial blight caused by Xanthomonas oryzae pv. oryzae (Xoo) leads to a substantial yield reduction of up to 50% in most rice-growing regions. Host plant resistance is an effective control method, and more than 30 resistance genes have been identified in rice genotypes. To understand the interaction of the pathogen in a susceptible reaction of the host plant, Xoo culture filtrate and treated culture filtrates were used to treat two rice genotypes using four strains Mai1, PXO88, Dak1 and Dak16. The study revealed that Xoo culture filtrate, heated culture filtrate and proteinase K treated culture filtrate induced typical bacterial blight symptoms on rice genotypes IRBB4 and FKR14 with a maximum lesion length of about 23.1 cm for culture filtrate. Heated culture filtrate phytotoxicity effects on both rice genotypes was with highest lesion length of about 6.9 cm, while 13.4 cm was the maximum length induced by a proteinase K treated fraction. After ethyl acetate treatment of the culture filtrate, a considerable reduction of the phytotoxicity was observed. Therefore we suggest that a low molecular-weight toxin may be present in the ethyl acetate extract should not play a major role in Xoo virulence and speculate that EPS, Xylanase, polygalacturonase, proteinaceouse contribute to Xoo virulence.