Inflammation causes discomfort, suffering and lower productivity of the victims. Synthetic anti-inflammatory drugs are not readily available and have adverse side effects. Alternative herbal medicines possess bioactive compounds that are safer and efficient in the management of various diseases and disorders. The present study evaluated for the anti-inflammatory activity of ethanol extracts of Castanopsis costata in rats to scientifically validate their traditional use among the Karo communities in Medan, Nort Sumatera. The plant samples were collected with the help of local herbalists in Namo Keling Village, Sumatera Utara and transported to Phytochemistry and Pharmacology laboratories, Tjut Nyak Dhien University, for cleaning, air drying, milling, and extraction. Wistar male albino rats of divided into six groups of 5 animals each; normal control, negative control, positive control and three experimental groups. The anti-inflammatory activity was tested using carrageenan-induced hind paw edema method. The anti-inflammatory activity of the extracts was compared to reference drug diclofenac. The leaf extract of C.costata reduced inflamed hind paw diameter of rats by between 26.09%-100% with a dose of 125 mg/kg BW during six days. The diclofenac reduced inflamed hind paw diameter by between 39.75%-100% with a dose of 4.5 mg/kg BW during six days. The qualitative phytochemical screening indicated the presence of alkaloids, flavonoids, glycosides, glycoside anthraquinones, steroids, tannins, and triterpenoids. The present study demonstrated potent anti-inflammatory activities of ethanol extracts of C. costata leaves in a dose-dependent manner, which supports their traditional use. The present study recommends the ethnomedicinal use of C.costata in the management of inflammation.