Background Lung cancer concerns a worldwide health problem and the efficacy of available treatments is unsatisfactory. Recently, thromboxane A2 (TXA2) synthase (TXAS) and receptor (TXA2R) have been documented to play a role in lung cancer development. Therefore, dual TXA2R modulator (i.e., the dual blocker of TXAS and TXA2R) may be more efficacious to kill lung tumor cells than single TXAS inhibitor or TXA2R antagonism. The close relationship between cyclooxygenase (COX)-2 and TXAS also raises whether or how TXA2 contributes to the oncogenic activity of COX-2. This study is therefore conducted to answer these questions. Methods Various inhibitors and siRNA were used to evaluate the roles of TXA2 and COX-2 in the proliferation and apoptosis of lung adenocarcinoma cells. Cell proliferation was detected using both MTS ELISA and BrdU labeling ELISA. Cell cycle distribution and apoptosis were examined by flow cytometric analysis. TXB2 level, reflecting the biosynthesis of TXA2, was detected by peroxidase-labeled TXB2 conjugates using an enzyme immunoassay kit. Western blotting was performed to evaluate many biomarkers for cell cycles, apoptosis and proliferation. The levels of COXs were screened by reverse transcriptase and real-time quantitative PCR. Results We found either single TXAS inhibitor/TXA2R antagonist or the dual TXA2 modulators offered a similar inhibition on cell proliferation. Moreover, inhibition of TXA2 arrested cells at the G2/M phase and induced apoptosis. It is further demonstrated that TXA2 was able to function as a critical mediator for tumor-promoting effects of COX-2 in lung adenocarcinoma cells. Conclusion The present study has for the first shown that dual TXA2 modulators and the single blocker of TXAS or TXA2R offer a similar inhibitory role in lung adenocarcinoma cell proliferation and that the tumor-promoting effects of COX-2 can largely be relayed by TXA2. Thus, TXA2 should be regarded as a critical molecule in COX-2-mediated tumor growth and a valuable target against lung cancer.