This study was carried out to investigate potential applications of the extract of Castanopsis cuspidata var. sieboldii NAKAI nut as a functional food ingredient. The pH and °Brix of nut were 6.43 and 3.17, respectively. L, a and b values as Hunter''s color were 83.07, 1.49 and 10.48, respectively. Total content of monosaccharide was 54.26 mg% and organic acids were composed of oxalic acid 495.37 mg%, formic acid 200.03 mg%, malic acid 93.65 mg%, citric acid 27.80 mg%, and succinic acid 16.61 mg%. Total phenolic contents in various solvent extracts were as follows: water 27.69 mg%, 75% ethanol 16.50 mg%, ethyl acetate 16.50 mg%, and methanol 10.30 mg%. The antioxidant activity (SC50, μg/mL) of the nut extracts by various solvents was in the order of ethyl acetate 74.88 〉methanol 155.00 〉n-hexane 213.33 〉ethanol 249.33 〉butanol 274.78 〉chloroform 314.67 〉75% ethanol 848.33 〉water extracts 869.67. The results indicated that the extract of C. cuspidata nut contained a potential food ingredient.