Insecticidal crystal protein gene cry1C which is highly toxic to Spodoptera exigua was cloned into an integrative vector pBMB-F7E, which was derived from Bacillus thuringiensis transposon Tn4430. The recombinant integrative plasmid pBMB-FLC harboring the cry1C gene was gained and transformed into a wild-type Bt strain YBT803-1. A transformant BMB803-A was obtained, and grown at 46 degrees C for about 120 generations, From which three recombinants with cry1C gene integrating into the chromosome were achieved at a frequency of approximately 3.4 x 10(-5). Southern blotting revealed that the integration occurred in different sites of the chromosome. The integrated cry1C were expressed effectively. The results of bioassays showed that the toxicity of recombinants BMB803-X and BMB803-Z against Plutella xylostella were similar to that of strain YBT803-1, and their toxicity to Spodoptera exigua were higher than that of strain YBT803-1.