Bacteriophage 029 produces its own DNA polymerase which is encoded by gene 2 [Watabe, K. and Ito, J. (1983) Nucleic Acid Res. 11, 8333]. This 029 DNA polymerase has been purified by phospho-cellulose, DEAE-cellulose, double-stranded DNA cellulose chromatography and glycerol gradient centrifugation. An exonuclease activity associated with the DNA polymerase was found through all the steps of the purification. This nuclease preferably degrades single-stranded DNA from the 3' to the 5' terminus direction, suggesting that the enzyme plays a role for proofreading during DNA replication. While DNA polymerase activity isolated from cells infected with temperature sensitive mutant of gene 2 is thermolabile, the nuclease activity is not significantly reduced at the restrictive temperature.