Objective To investigate the chemical constituents of Dimocarpus longan seeds in Sapindaceae.Methods The chemical constituents were isolated from the ethanol extract of D.longan seeds by silica gel column chromatography.Their structures were identified on the basis of physical and chemical properties and spectral analysis.Results One compound was isolated and identified as 2-methyl-1,10-undecanediol,named longandiol(1).Conclusion Compound 1 is a new compound.