The study on the “Effect of medicinal plant extract treatment toBmNPV polyhedral bodieswas undertaken in the Department of Sericulture UAS, GKVK, Bangalore. The polyhedral bodies treated with aqueous extracts of different medicinal plants viz., Adathodavasica, Bougainvillea spectabilis, Phyllanthusniruri, Terminaliaarjuna and Pongamiaglabra administered to silkworm through mulberry leaves once during fourth and fifth instar larvae of PM x CSR2 recorded significantly higher mature larval weight of fourth and fifth instar administered batches of PMxCSR2. The higher mature larval weight (27.85 and 28.68 g) was recorded in P. niruri administered lots followed by B. spectabilis (27.18 and 27.90 g), T.arjuna (26.93 and 27.34 g), A. vasica (26.36 and 27.07 g) and P. glabra (26.31 and 26.46 g) than control (25.82 and 25.65 g). However minimum fifth instar larval duration and total larval duration was recorded in P. niruri (8.12 and 7.90 days; 28.20 and 29.02 days) and maximum duration was noticed in P. glabra (9.10 and 9.04 days; 29.24 and 30.16 days). The effect of P. nirurion fourth instar larvae of PMxCSR2 was found less (8.50 %) followed by B. spectabilis (11.50 %), T. arjuna (12.25%), A. vasica(13 %) and P. glabra (13.50 %) they were found on par with each other. The water control lots recorded only 8 per cent of total mortality which was significantly lower than that of botanical treatment. In fifth instar the effect was found vivid from the experiment that, viral dilution and hours of treatment resulted decreased mortality from 15.33 to 9.00 and 14.16 to 7.66 per cent was recorded for 10-1 and 10-3 respectively.