Baculoviral expression systems, including those of Autographa californica multiple nucleopolyhedrovirus Bombyx mori nucleopolyhedrovirus (BmNPV), are used for recombinant protein production. Four B. mori-derived (BmN4, Bm5, Bmc140, and Bme21) cell lines were infected with recombinant BmNPV viruses expressing firefly luciferase or EGFP as reporters under the control of a viral polyhedrin promoter. Bme21 exhibited significantly higher (100-fold) luciferase activity than BmN4 and Bm5. With the EGFP reporter protein, Bme21 cells showed a marked increase in the ratio of EGFP-positive cells, reaching 90 % on day 4 post-infection, while Bm5 and BmN4 cells had a slow increase in the ratio of their EGFP-positive population. The viral titer in a supernatant of Bme21 cell culture increased faster than those of Bm5 and BmN4 cells. This susceptibility indicates that the Bme21 cell line is useful for large-scale protein expression using BmNPV.