We have developed a parallel, rapid, high-throughput oligonucleotide microarray-based assay for the reliable detection and genotyping of three cry genes (cry1, cry2 and cry9) in Bacillus thuringiensis (Bt). After the non-polymerase chain reaction (PCR), amplified Bt genomic DNA were fluorescent-labeled using a random primer. The corresponding oligonucleotide probes were designed for the different cry genes that can hybridize Bt genomic DNA after cluster analysis and were printed on glass slides. This microarray has unambiguously detected and identified the cry genes in 10 isolates and reference Bt. Our data demonstrates that the microarray assay is simple and rapid for the detection and genotyping of genes. This type of assay is also a potentially valuable tool for identification and characterization of bacterial functional genes in general.