The expression of a fusion protein comprised of two Bacillus thuringiensis crystal proteins, lepidopteran toxic CrylAc and dipteran toxic Cry11A, in B. thuringiensis Cry-B strain was examined. To construct a recombinant gene, the cry11Α gene was inserted behind the ΧhoI site in the middle region of the crylΑc gene, but the C-terminal fragment (structure fragment) of CrylAc was removed in fusion construction (pProAcN-11A). Also, the cry 11A gene was singly cloned under the crylΑc promoter (pPro11A). The Β. thuringiensis Cry-B strain with pProAcN-11A (ProAcN-11A/CB) produced ovoid shaped parasporal inclusions of relatively small size, while Pro11A/CB produced rhomboid shaped ones. Unexpectedly, ProAcN-11A/CB produced a protein of approximately 60 kDa while Pro11A/CB and ProAc/CB produced typical 72 kDa and 130 kDa proteins, respectively. However, ProAcN-11A/CB exhibited significant dual toxicity on larvae from two insect orders, 72.7% on Plutella xylostella and 65.5% on Culex pipiens. The current results suggest that expression and crystallization of a fusion protein between toxic fragment of CrylAc and Cry11A was incomplete in the Cry-B strain though ProAcN-11A/CB produced parasporal inclusions and had dual toxicity.