Overexpression of mammalian 2-Cys peroxiredoxin (Prx) enzymes is observed in most cancer tissues. Nevertheless, their specific role in colorectal cancer progression has yet to be fully elucidated. Here, a novel molecular mechanism by which PrxII/TNKS interaction mediates survival of APC-mutant CRC cells was explored. In mice with inactivating APC mutation, a model of spontaneous intestinal tumorigenesis, deletion of PrxII reduces intestinal adenomatous polyposis and thereby increases survival. In APC mutation-derived human CRC cells, PrxII depletion hinders the PARP-dependent Axin1 degradation through TNKS inactivation. H2O2-sensitive Cys residues in zinc-binding domain of TNKS1 was found to be crucial for its PARsylation activity. Mechanistically, direct binding of PrxII to ARC4/5 domains of TNKS confers a vital redox protection against TNKS oxidative inactivation. As a proof-of-concept experiment, a chemical compound targeting PrxII inhibits the growth of tumors xenografted with APC-mutation-positive CRC cells. Collectively, the results provide evidence revealing a novel redox mechanism for regulating TNKS activity in such that physical interaction between PrxII and TNKS promotes survival of APC-mutant colorectal cancer cells by PrxII-dependent antioxidant shielding.