In order to better understand the fundamental biology of Bacillus thuringiensis, a single oligonucleotide primer (50-CATSSCCATCAASYTAAVR-30) was used to investigate the distribution pattern of IS231 elements in B. thuringiensis by PCR. Theresults indicated that IS231 elements appeared in 20 standard strains and 107 of 111 China isolates. Three novel IS231, IS231J,IS231O and IS231Q, five variants and a mobile insertion cassette MICBth4 were cloned from eight standard strains of B. thuringiensis,respectively. Interestingly, BLAST analysis revealed that the 50 end of novel IS231J shared 99% identity in 495-bp with aDNA segment adjacent to the 30 end of B. thuringiensis vip1Ac gene (GenBank Accession No. AY245547). Two phylogenetic treesof IS231 elements were constructed and analyzed by neighbor-joining and UPGMA methods from PHYLIP 3.6b program,respectively.