Nucleopo9lyhedrovirus (NPV) of the satin moth Leucoma Stilpnotia) salicis L. was produced by infecting the larvae with the LesaNPV strain obtained from epizootic center in Katowice. The infected larvae were reared under laboratory, greenhouse and insectarium conditions. Because L. salicis can not be reared on a semi-synthetic food, the insects were maintained on natural products. Efficiency of the mass virus production depended on an insect growth stage, virus concentration and number of infected larvae in a rearing container. The fourth-instar larvae were the best for LesaNPV replication. Inoculation of younger larval stages (third instar stadium) provided less number of inclusion bodies (insects were dying sooner and did not meet their maximum body weight). On the contrary inoculation of older stages (fifth and sixth instars) resulted in slower virus replication and low larva mortality. The virus concentration of 3 x 10 9 of inclusion bodies per container was the optimum inoculum for the mass virus production (double infection with the virus concentration of 1.5 x 10 9 inclusion bodies/1000 larvae). The larvae reared at high-density became more infected and it caused their earlier death and in consequences low virus efficiency. Rearing the insect at low density (less than 10 larvae per 1.0 L container) was conducive for both an increase of insect body mass and virus replication as well. The highest number of inclusion bodies per one larva(5.3 x 10 9 – 7.7 x 10 9) and the highest total number of inclusion bodies (152 x 10 11 – 188 x 10 11) were achieved under these rearing conditions in a greenhouse and insectarium.