4-[(1,2-dihydro-2-oxo-3H-indol-3-ylidene)amino]-N(4,6-dimethyl-2-pyrimidiny)benzene sulphonamide and its derivatives were evaluated for antiviral activity against Pathogenic viruses such as Hepatitis C Virus and SARS-CoV in Vero and Huh 5-2 cells, respectively. The 5-fluoro derivative inhibited the HCV RNA synthesis at 6 μg/ml, without toxicity at a concentration up to 42 μg/ml in Huh 5-2 cells. Among the compounds tested SPIII-5F exhibits the 45% maximum protection against replication of SARS-CoV in Vero cells.