The antioxidative activity of Alpinia oxyphylla was investigated through measuring the radical scavenging effect on 1,1-diphenyl-2-picrylhydrazyl (DPPH) and inhibitory activity for linoleic acid peroxidation. Two antioxidative diarylheptanoids, yakuchinone A (1) and oxyphyllacinol (2), were isolated from the fruits of A. oxyphylla using thin layer chromatography (TLC) autographic assays. The DPPH scavenging activities of the compounds ($IC_{50}=1$, $57{pm}2.1;{mu}M$; 2, $89{pm}3.1;{mu}M$) were lower than vitamin C ($IC_{50}=51{pm}1.1;{mu}M$), but higher than butylated hydroxytoluene (BHT, $IC_{50}=99{pm}2.2;{mu}M$). Also, inhibitory activities for linoleic acid peroxidation of the compounds ($IC_{50}=1$, $0.19{pm}0.011;mM$; 2, $0.31{pm}0.009;mM$) were higher than those of vitamin C ($IC_{50}=0.59{pm}0.017;mM$) and BHT ($IC_{50}=0.52{pm}0.014;mM$). In addition the $^{13}C-NMR$ data of oxyphyllacinol (2) have been first reported in this paper.