To investigate the expression efficiency of new transfer vector of Bombyx mori nuclear polyhedrosis virus (BmNPV), Escherichia coli lacZ gene was inserted into new transfer vector pBmKSK1, under the control of polyhedrin promoter and expressed in BmN-4 cells and larvae of silkworm, Bombyx mori. The recombinant virus containing lacZ gene was isolated from BmN-4 cells coinfected with transfer vectro pBmKSK1-LacZ and wild type BmNPV genome, and analysed by Southern blotting. The expression of ${eta}$-galactosidase was characterized by SDS-PAGE, Western blotting and ${eta}$-galactosidase activity assay. The results showed that the level of expression in silkworm larvae was higher than that of BmN-4 cells.