Activation of Akt, or protein kinase B, is frequently observed in human cancers. It has been demonstrated that PI3K activation leads to radiation resistance. Here, the role of PI3K/Akt/COX-2 pathway in the resistance to radiation in human cervical cancer HeLa cells is explored. Cultured HeLa cells were randomly assigned to five treatment groups: control, radiation, LY294002, PI3K antagonist, and the COX-2-antagonist celecoxib, with the objective of determining the role of PI3K/Akt/COX-2 pathway in the radiation resistance of HeLa cells. The cell survival ratios were computed by clone formation. To calculate the quasi-threshold dose (Dq), mean lethal dose (D(0)), survival fraction at 2 Gy radiation dose (SF(2)), and radiosensitization ratio, the cell survival curves were fitted to the one-hit multitarget model. The protein expression profiles for pAkt, Akt, COX-2, Bad, and pBad were detected by Western blot analysis, and the mRNA expression profiles for COX-2 and Bad were analyzed by RT-polymerase chain reaction. Treatment with a combination of celecoxib, LY294002, and radiation resulted in elevated Dq, D(0), and SF(2), and increased radiosensitivity in HeLa cells. The PI3K/Akt/COX-2 pathway was activated by radiation, whereas celecoxib inhibited the activation of the PI3K/Akt/COX-2 axis through several targets. Our results indicate that the activated PI3K/Akt/COX-2 signal transduction pathway was the main cause for decline in radiosensitivity in HeLa cells. This study proposes that the inhibition of the PI3K/Akt/COX-2 pathway can synergistically enhance radiation efficacy.