Celecoxib, a selective cyclooxygenase-2 (COX-2) inhibitor, has been reported to exert chemopreventive and antitumor effects on colon cancer, one of the most common solid epithelial malignancy worldwide. The aim of this study was to elucidate whether celecoxib may be able to affect epithelial–mesenchymal transition (EMT), a critical process involved in cancer cell invasiveness and metastasis and then proposed to be relevant for cancer progression. Human HT-29 colon cancer cells were exposed to carefully controlled hypoxic conditions and/or epidermal growth factor (EGF) and then investigated for EMT changes and signal transduction pathways involved by using morphological, molecular, and cell biology techniques. Celecoxib inhibited basal and EGF-stimulated proliferation, hypoxia-related HIF-1α recruitment/stabilization as well as hypoxia- and EGF-dependent activation of ERK and PI3K. Interestingly, celecoxib prevented EMT-related changes, as shown by modifications of β-catenin intracellular localization or vimentin and E-cadherin levels, as well as HT-29 invasiveness induced by hypoxia, EGF, or hypoxia plus EGF. Finally, experiments performed on SW-480 colon cancer cells (i.e., cells lacking COX-2) exposed to hypoxia, used here as a stimulus able to induce EMT and invasiveness, revealed that in these cells celecoxib was ineffective. Results of the present study indicate that celecoxib has the potential to negatively affect induction of EMT and increased invasiveness of colon cancer cells as elicited by different signals originating from tumor microenvironment (i.e., hypoxia and EGF). Moreover, these effects are likely be related to the pharmacological inhibitory effect exerted on COX-2 activity. © 2011 Wiley Periodicals, Inc.