One hundred twenty one isolates of Bacillus thuringiensis were isolated from 91 soil samples collected in the national park and wildlife sanctuary in Krabi province. All isolates of B.thuringiensis were tested for their insecticidal activity against Spodoptera litura, S. exigua and Plutella xylostella larvae. Seven isolates of B. thuringiensis named JCPT7, JCPT16, JCPT18, JCPT64, JCPT68, JCPT74 and JCPT89 exhibited toxic activities against the insects, more than 90% mortality. The detection of cry gene of these isolates was done by a method based on polymerase chain reaction (PCR). The PCR result indicated that cry1Ab, cry1Ac, cry1C, cry1D, cry1I, cry9A, cry9B and cry2A were on chromosomal DNA and cry1Aa, cry1Ab, cry1Ac, cry1C, cry1D, cry1I and cry2A were on plasmid DNA. This study has introduced the promising B. thuringiensis isolates collected from soil samples which could be developed as an effective biocontrol agent for Lepidopterous pest.