Cyclooxygenase-2 (COX-2) has been reported to be associated with tumor development and progression as well as to protect cells from apoptosis induced by various cellular stresses. Through a tetracycline-regulated COX-2 overexpression system, we found that COX-2 inhibits detachment-induced apoptosis (anoikis) in a human bladder cancer cell line, EJ. We also found that the inhibition of anoikis by COX-2 results from activation of the PI-3K/Akt pathway as evidenced by suppression of the COX-2 effect on anoikis by a PI-3K inhibitor, LY294002. Furthermore, COX-2 enhanced Mcl-1 expression in the anoikis process, implying that Mcl-1 also may be involved in mediating the survival function of COX-2. Together, these results suggest that COX-2 inhibits anoikis by activation of the PI-3K/Akt pathway and probably by enhancement of Mcl-1 expression in human bladder cancer cells. This anti- anoikis effect of COX-2 may be a part of mechanisms to promote tumor development and progression.