Cyclooxygenase-2 (COX-2), an important enzyme, plays a pathological role in diseases, which can be inhibited by proanthocyanidins (PCs) effectively. In this paper, we investigated the inhibitive mechanism of COX-2 performed by PCs. Reverse transcription-polymerase chain reaction (RT-PCR) was performed to identify the mRNA expression level of COX-2 in A549 cell, which was induced by interleukin-1 beta (IL-1β). The pGL3 luciferase reporter vector containing the COX-2 gene promoter fragment (pGL3/COX-2p) was transfected into A549 cell induced by IL-1β, the interference on the COX-2 promoter activity from PCs was analyzed using a dualluciferase reporter assay, and the expressions of the nuclear factor κB composed of subunit p65 (NF-κB/p65) and the inhibitor-κB (I-κB) were measured by the Western blotting and immunocytochemistry. The results exhibited that PCs not only inhibited the transcript of COX-2 mRNA and the COX-2 promoter activity, but also suppressed the nuclear translocation of NF-κB/p65 protein and the degradation of I-κB protein.