DNA bases carrying an exocyclic amino group, namely adenine (A), guanine (G) and cytosine (C), encounter deamination under nitrosative stress. Oxanine (O), derived from deamination of guanine, is a cytotoxic and potentially mutagenic lesion and studies of its enzymatic repair are limited. Previously, we reported that the murine alkyladenine glycosylase (Aag) acts as an oxanine DNA glycosylase (JBC (2004), 279: 38177). Here, we report our recent findings on additional oxanine DNA glycosylase (ODG) activities in Aag knockout mouse tissues and other mammalian tissues. Analysis of the partially purified proteins from the mammalian cell extracts indicated the existence of ODG enzymes in addition to Aag. Data obtained from oxanine DNA cleavage assays using purified human glycosylases demonstrated that two known glycosylases, hNEIL1 and hSMUG1, contained weak but detectable ODG activities. ODG activity was the highest in hAAG and lowest in hSMUG1.