The Tth DNA polymerase gene from the thermophilic Thermus thermophilus (strain HB8) was amplified, cloned and expressed in Escherichia coli. The recombinant DNA polymerase containing a polyhistidine tag at the N-terminus was isolated in a single step by Ni2+ affinity chromatography. The purified recombinant enzyme, showing high polymerase activity contained 43 additional amino-acid residues (including a cluster of six histidine residues inserted for purification of the recombinant protein by metal-affinity chromatography) at N-terminus. The applied overexpression system was very efficient giving 700,000 u of DNA polymerase activity from 1 liter of induced culture. The enzyme was characterized and displayed high DNA polymerase and reverse transcriptase activities and high thermostability as compared to the native Tth DNA polymerase.