An efficient and simple method for constructing an environmental library using mechanically sheared DNA obtained directly from geothermal sediments is presented. The method is based on blunt-end modification of DNA fragments followed by 3'-adenylation using Vent DNA polymerase and Taq DNA polymerase, respectively. The prepared DNA fragments are then ligated into a TA cloning vector and used in the transformation of Escherichia coli. This method has been successfully applied to the cloning of ORFs derived from uncultivated prokaryotes present in geothermal sediment.