P66shc protein is an alternative transcript product of the SHC1 gene. Whereas two other isoforms (p52shc and p46shc) have adaptor function in the RAS signaling pathway, p66shc regulates the amount of reactive oxygen species (ROS) in a cell. Previously, it was demonstrated that the p66shc genome knockout significantly extends maximal lifespan in mice. P66shc could translocate into the mitochondria and increase intracellular ROS level, although basic mechanisms of this activity remain poorly understood. P66shc seems to play a significant role in carcinogenesis since an increased expression of p66shc correlates with poor prognosis in colorectal carcinoma. In our study, we applied RNA interference using lentiviral constructions that express short hairpin RNA (shRNA) against the N-terminal CH2 domain of the p66shc isoform. As a consequence, the p66shc but not p52shc and p46shc isoforms was selectelively suppressed in the RKO colon carcinoma cell line. We found that RKO cells with p66shc knockdown have been shown to be more resistant to oxidative stress induced by hydrogen peroxide exposure or serum starvation. Moreover, mitochondrial fragmentation that depends on mitochondrial ROS amount was significantly decreased in p66shc-deficient RKO cells. Our findings are the consistent with the hypothesis that p66shc participates in mitochondrial accumulation of during oxidative stress ROS and consequently promotes induction of apoptosis.