In 1901, a unique bacterium was isolated as a pathogen of the sotto disease of the silkmoth larvae, and later in 1915, the organism was described as Bacillus thuringiensis. Since the discovery, this bacterium has widely attracted attention of not only insect pathologists but many other scientists who are interested in strong and specific insecticidal activity associated with inclusion bodies of B. thuringiensis. This has led to the recent worldwide development of B. thuringiensis-based microbial insecticides and insect-resistant transgenic plants, as well as the epoch-making discovery of parasporin, a cancer cell-specific cytotoxin. In the review, we introduce a detection study of interaction between inclusion proteins of B. thuringiensis and brush border membrane of insects using surface plasmon resonance-based biosensor, and then identification and cloning of parasporin-4, a latest cancer cell-killing protein produced by B. thuringiensis A1470 strain. Inclusion bodies of the parasporin-4 produced by recombinant Escherichia coli were solubilized and activated with a new method and purified by an anion-exchange chromatography. At last the characterization of the recombinant parasporin-4 was shown.