Cyclooxygenase-2 (COX-2) has been shown to be upregulated in a variety of tumors so that COX-2 may be a potential target in the treatment of cancer. In order to further explore the mechanism, we used RNA interference to study effects of the inhibition of COX-2 on esophageal squamous cell carcinoma (ESCC) lines. Western blot analysis demonstrated that COX-2 expression was significantly reduced in ESCC cells treated with the COX-2-specific siRNA. Furthermore, the COX-2 siRNA treatment inhibited cell proliferation and induced apoptosis in ESCC cells. In addition, the combination treatment of COX-2 siRNA and acidum acetil salicylicum (aspirin) has a synergistic effect. Therefore, this combination has potential as an anticancer therapy for the treatment of ESCC.