A cDNA of a mutant (K151E, R154G) of single chain urokinase-type plasminogen activator (mscu-PA) was constructed to include the natural scu-PA signal peptide sequences and transferred into the genome of Bombyx mori nuclear polyhedrosis virus (BmNPV) by transfer vectors pBE284 (derived from BmNPV) and pVL1392 (from AcNPV), respectively. Both Bombyx mori (BmN) cells and silkworm larvae were infected with the two recombinant viruses. Fibrin-plate assay showed that the re-virus from pVL1392 increased the yield of mscu-PA three times compared with the re-virus from pBE284.