The Bacillus thuringiensis strain K4 was isolated from fallen leaves, sampled in a forest region of the city of Mungyeong, Korea. The flagellated vegetative cells of B. thuringiensis strain K4 were agglutinated with the H3 reference antiserum and further, agglutinated with 3b and 3d monospecific antisera but non-reactive for 3c and 3e factor sera. These results create a new serogroup with flagellar antigenic structure of 3a3b3d, designated serovar mogi. The strain K4 showed high activity against dipteran larvae, Anopheles sinensis and Culex pipiens pallens while no lepidopteran toxicity. It produced a single ovoidal-shaped parasporal crystal whose SDS-PAGE protein profile consisted of several bands ranging from 75 to 30 kDa. Through the protein identification by nano-LC-ESI-IT MS analysis, the putative peptides of Cry19Ba, Cry40ORF2, Cry27Aa and Cry20Aa were detected. In contrast to the plasmid profile of B. thuringiensis H3 serotype strains, the strain K4 contained only a large plasmid (~100 kb) and we cloned partial cry27Aa, cry19Ba and cry40ORF2 genes from it by thermal asymmetric interlaced PCR. Sequencing analysis showed 87%, 88% and 88% homologous with known cry27Aa, cry19Ba and cry40ORF2 genes, respectively. The new type strain, B. thuringiensis subsp. mogi (H3a3b3d) will be a good resource for new mosquitocidal cry genes.