Antiviral activity of dasyscyphin C (C28H40O8) extracted from leaves of Eclipta prostrata was evaluated against fish nodavirus, grouper nervous necrosis virus (GNNV) infected SIGE (Sahul Indian Grouper Eye) cell lines under in vitro conditions. Nodavirus infection to SIGE cells was confirmed by cytopathic effect (CPE) and reverse transcriptase-polymerase chain reaction. The susceptibility of the virus to the isolated compound was confirmed by measuring the virus titre (TCID50/ml) at every 24 hrs. The isolated compound was found to be effective in inhibiting the proliferation of fish nodavirus (FNV) infected in the SIGE cell lines at 20μg/mL and the cell viability was decreased to 22% as determined by MTT assay. The virus titre (TCID50/ml) was 3.7 at the end of 7th day in dasyscyphin C treated SIGE cells post inoculated with nodavirus. Based on the results it can be concluded that dasyscyphin C may be used as antiviral agent against fish nodavirus. © 2010 Krishnan K, et al.