An experimental study was undertaken to quantify the effects of insect hormones on the replication of nucleopolyhedrovirus (NPV). The results demonstrated that TCID/ sub 50/ at 72 h post-infection (hpi) rose systematically from 0.55$ imes$10$^{8}$ /m1, for untreated cells, up to 1.67$ imes$10$^{8}$ / ml at 3$mu$g/ml, then dropped down to 1.45$ imes$10$^{8}$ /m1 at 4 $mu$g/ml, by adding ecdysone to the culture medium for Bm-N cells infected with a wild-type Bambyx mori. nucleopolyhedrovirus (BmNPV). The optimum enhancement of about 3 times on budded virus (BV) titer at 72 hpi was given at 3 $mu$g/ml of ecdysone. While the polyhedra number had no obvious variation within the range of concentrations from 0 to 4 $mu$g/ml. By addition of juvenile hormone analogue (JHA) into the media with this concentration range, the BmNPV TCID/ sub 50/ and polyhedra number at 72 hpi did not show significant changes. Also, the addition of either 3 $mu$g/ml of ecdysone or 3 $mu$g/ml of JHA to the culture media did not appear to affect the TCID/ sub 50/ and polyhedra number significantly in infected Sf-21 cells with the autographa californica nucleopolyhedrovirus (AcMNPV).