Cisplatin is one of the major chemotherapeutic weapons used against different human cancers, although its mechanism to induce apoptosis is not fully understood. The presence of wild type p53 has been suggested to be important for cisplatin cytotoxicity, hence we found that cisplatin induced apoptosis in cell lines with functional p53. Using the HCT116 colon carcinoma derived cell line we have established that the apoptotic activity of cisplatin requires the onset of a p53-mediated p38α MAPK pathway through generation of reactive oxygen species (ROS). HCT116 p53-deficient cells were much less sensitive to apoptosis by cisplatin than their p53wt counterparts, where apoptosis was strongly inhibited by antioxidants. Moreover, the presence of pifithrin-α, an inhibitor of p53 transcriptional activity, blocked cisplatin-induced apoptosis, reduced the generation of ROS produced upon cisplatin treatment. In addition, we have identified p38α as the isoform necessary for cisplatin-induced apoptosis, upon activation by p53-mediated ROS production. p38α MAPK contributes to further activation of p53, which leads to a positive feedback loop, p38α MAPK/p53. We conclude that the p53/ROS/p38α MAPK cascade is essential for cisplatin-induced cell death in HCT116 cells and the subsequent p38α/p53 positive feedback loop strongly enhances the initial p53 activation.