The efficacy of wood ash from Terminalia arjuna (arjun) and T. tomentosa (asan) has been tested against virosis of tasar silkworm, Antheraea. mylitta D. The Polyhedral Occlusion Bodies (POBs) of Cytoplasmic Polyhedrosis Virus of A. mylitta (AmCPV) were exposed to the aqueous solution (0.5 to 4%) of wood ash for 5 to 30 minutes. The treated suspension of POBs was orally inoculated once to tasar silkworm larvae after 24 hours of $1^{st}$ moult, and larvae reared in indoor on arjun leaves till spinning. The application of aqueous solution of wood ash has established its potential as antiviral agent against cytoplasmic polyhedrosis virus. Two percent aqueous solution of wood ash from arjun and asan dissolved the Polyhedral Occlusion Bodies (POBs) of cytoplasmic polyhedrosis virus of tasar silkworm and inactivated the virions within a short period of 20 to 30 minutes. In vivo efficacy of aqueous solution of wood ash resulted in reduction of larval mortality due to virosis. The mortality was reduced to $2.56{pm}0.21;and;3.03{pm}0.32%$ when treatment of 2.0% solution of wood ash of arjun and asan respectively were applied for 20 minutes, compared to inoculated control $(92.18{pm}7.52%)$. No mortality was recorded when treatment of 2.5% solution of wood ash of arjun and asan were applied for 10 minutes or more.