Bcl2 and c-Myc are two major oncogenic proteins that can functionally promote DNA damage, genetic instability and tumorigenesis. However, the mechanism(s) remains unclear. Nitrosamine 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanone (NNK) is the most potent carcinogen contained in cigarette smoke that induces cellular DNA damage. Here we found that Bcl2 potently suppresses the repair of NNK-induced abasic sites of DNA lesions in association with increased c-Myc transcriptional activity. Bcl2’s BH4 domain (aa 6-31) was found to bind directly to c-Myc’s MBII domain (aa 106-143) and this interaction is required for Bcl2 to enhance c-Myc transcriptional activity and inhibit DNA repair. In addition to mitochondria, Bcl2 is also expressed in the nucleus where it co-localizes with c-Myc. Expression of nuclear-targeted Bcl2 enhances c-Myc transcriptional activity with suppression of DNA repair but fails to prolong cell survival. Depletion of c-Myc expression from cells overexpressing Bcl2 significantly accelerates the repair of NNK-induced DNA damage, indicating that c-Myc may be essential for Bcl2’s effect on DNA repair. It is known that APE1 plays a crucial role in the repair of abasic sites of DNA lesions. Since overexpression of Bcl2 results in up-regulation of c-Myc and down-regulation of APE1, this suggests that APE1 may function as the downstream target of Bcl2/c-Myc in the DNA repair machinery. Thus, Bcl2, in addition to its survival function, may also suppress DNA repair in a novel mechanism involving c-Myc and APE1, which may lead to an accumulation of DNA damage in living cells, genetic instability and tumorigenesis.