Human cervical cancer oncogene 1, HCCR-1, is over-expressed in various human tumors and appears to serve as a negative regulator of the p53 gene. HCCR-1 transgenic mice developed breast cancers but it is unknown how HCCR-1 contributes to tumorigenesis. We identified the HCCR-1 binding protein 3 (HCCRBP-3) as a binding partner for HCCR-1. These two proteins co-localized to the mitochondria. HCCRBP-3 over-expressed in various human tumors converted normal cells into tumor cells in vitro. Nude mice injected with NIH/3T3 cells stably transfected with HCCRBP-3 also induced the tumor formation. In addition, p53 showed the functional impairment in HCCRBP-3-transfected cells as accompanied with defective induction of p21 and bax. In support of this, p21 promoter activities containing p53 responsive elements were inhibited by HCCRBP-3 in a dose-dependent manner. Therefore, our study suggests that HCCRBP-3 contributes to the HCCR-1 induced tumorigenesis by interrupting the p53 function. © 2013 Wiley Periodicals, Inc.