Rheum undulatum L. has been used as Rhei Radix in Korean Pharmacopea although their pharmacological effects were not studied much. In this studym, we tested anti-inflammatory effect as a representative activity of Rheum undulatum L. extracts using cyclooxygenase (COX)-2 inhibition. Murine macrophage, Raw 264.7 cells were incubated with lipopolysaccharide (1 $mu extrm{g}$/ml) to induce COX-2. The prostagladin $E_2$ ($PGE_2$) levels as an indicator of COX-2 activity were determined in the culture medium using ELISA. Inhibition of acetylsalicylic acid (ASA) as a standard, aloe-emodin, chrysophanol, rhein, 80% ethanol extract of Rheum undulatum L. (Ex) and ether fraction (Fr) after acid hydrolysis of Rheum undulatum L. were tested in induced COX-2 described above. $IC_{50}$ values were 0.082 $mu extrm{g}$/ml for ASA. 181 $mu extrm{g}$/ml for aloe-emodin, 3.65 $mu extrm{g}$/ml for emodin, 144 $mu extrm{g}$/ml for chrysophanol, 39.8 $mu extrm{g}$/ml for rhein, 141 $mu extrm{g}$ of herb/ml for Ex, and 95.7 $mu extrm{g}$ of herb/ml for Fr. We found that Ex and Fr of Rheum undulatum L. were more effective than other anthraquinones, since their $IC_{50}$ are lower than others.