Six new serovarieties of B. thuringiensis carrying specific H-antigen have minor differences in biochemical characteristics and morphological characteristics of crystals, which are commonly resistant against four antibiotics. The B. thuringiensis serovar. coreanensis is nontoxic to silkworm larvae, but it is moderately toxic against the Culex pipiens larvae. The B. thuringiensis serovar. konkukian and leesis are nontoxic against mosquitos larvae, but are toxic against silkworm larvae. The B. thuringiensis serovar. seoulensis, sooncheon, and yosoo are highly toxic to B. mori larvae and moderately toxic to C. pipiens larvae. The six serovarieties harbor different plasmid DNA patterns. A 102-kDa protein is a major crystal protein in the four serovarieties and a 86-kDa protein is in one serovariety.