In this study seventy-three Bacillus thuringiensis strains were isolated from soil samples collected from eleven hazelnut fields in the north-east coast of Turkey. They were characterized by morphological, biochemical and molecular methods and tested for insecticidal activity to find out the relatively more effective and safe biological control agents against some plant pests, especially hazelnut pests. A total of 40 of the B. thuringiensis strains fit the internally transcribed spacers (ITSs) characterisation of the B. thuringiensis varieties known. Repetitive extragenic palindromic-PCR (rep-PCR) results indicate that there is a significant genomic variation among the B. thuringiensis isolates. Experimental infections were carried out to detect the insecticidal effect of the isolates against three important pests, Hyphantria cunea, Agalastica alni and Neodiprion sertifer from three different orders. Twenty five of the 73 isolates under study showed high insecticidal effect against H. cunea, 10 against A. alni and 25 against N. sertifier and 2 against all the three insects. Four isolates were pathogenic for A. alni and H. cunea.