The inhibition of Interleukin-1beta (IL-$1{eta}$) is of substantial interest for the treatment of rheumatoid arthritis. Using an in vitro assay with RAW 264.7 cells, oxo-acetic acid 2-ethoxy-4-(3-hydroxy-2-oxopropyl) phenyl ester (1) was isolated from the roots of Paeonia suffruticosa Andrews as an inhibitor of IL-$1{eta}$ with an $IC_{50}$ value of 56 ${mu}M$. Compound 1 is a novel phenylesteric compound from P. suffruticosa Andrews. Compound 1 was shown to inhibit the production of pro-inflammatory cytokines in RAW 264.7 cells. Thus, a possible new action of novel compound is provided explaining the anti-rheumatoid arthritic properties of P. suffruticosa Andrews.