The possibility that Escherichia coli MutT and human MTH1 (hMTH1) hydrolyze oxidized DNA precursors other than 8-hydroxy-dGTP (8-OH-dGTP) was investigated. We report here that hMTH1 hydrolyzed 2-hydroxy-dATP (2-OH-dATP) and 8-hydroxy-dATP (8-OH-dATP), oxidized forms of dATP, but not (R)-8,5'-cyclo-dATP, 5-hydroxy-dCTP, and 5-formyl-dUTP. The kinetic parameters indicated that 2-OH-dATP was hydrolyzed more efficiently and with higher affinity than 8-OH-dGTP. 8-OH-dATP was hydrolyzed as efficiently as 8-OH-dGTP. The preferential hydrolysis of 2-OH-dATP over 8-OH-dGTP was observed at all of the pH values tested (pH 7.2 to pH 8.8). In particular, a 5-fold difference in the hydrolysis efficiencies for 2-OH-dATP over 8-OH-dGTP was found at pH 7.2. However, E. coli MutT had no hydrolysis activity for either 2-OH-dATP or 8-OH-dATP. Thus, E. coli MutT is an imperfect counterpart for hMTH1. Furthermore, we found that 2-hydroxy-dADP and 8-hydroxy-dGDP competitively inhibited both the 2-OH-dATP hydrolase and 8-OH-dGTP hydrolase activities of hMTH1. The inhibitory effects of 2-hydroxy-dADP were 3-fold stronger than those of 8-hydroxy-dGDP. These results suggest that the three damaged nucleotides share the same recognition site of hMTH1 and that it is a more important sanitization enzyme than expected thus far.