Torreya grandis cv. Merrillii is an endemic tree species in China, seeds of which are used as a popular snack, possessing beneficial effects on preventing angiosclerosis and coronary heart diseases. In this study, antioxidant activity and chemical constituents of T. grandis cv. Merrillii seed (TGMS) were investigated. The antioxidant activity of different fractions and the ethanol extract was evaluated using 1, 1-diphenyl-2-picrylhydrazyl (DPPH) radical scavenging capacity, hydroxyl radical scavenging activity and lipid peroxidation assays. The oil, CH2Cl2 and n-BuOH fractions, and ethanol extract of TGMS all showed antioxidant activities in these models, especially the DPPH one. By GC-MS analysis, twenty-seven constituents were identified from the oil fraction of TGMS. The total content of phenolic compounds in the CH2Cl2 and n-BuOH fractions and ethanol extract was also determined by the Folin-Ciocalteau method as 17.6, 21.6 and 12.9 microg/mg, respectively. In addition, analysis of the CH2Cl2 fraction yielded four phenolic compounds: 4-hydroxybenzaldehyde, 4-methoxy pyrocatechol, coniferyl aldehyde, 4-hydroxy cinnamaldehyde, and two steroids, beta-sitosterol and daucosterol. These results provide scientific support for the empirical use of TGMS as a medicinal food for cardiovascular diseases.