The determination of trace levels of aluminum by high performance liquid chromatography (HPLC) with spectrophotometric detection using quercetin, a bioactive substance as a pre-column reagent, is developed in this paper. The Al-quercetin chelate was separated on a reversed-phase ODS column with a mobile phase consisting of 70% water (pH 1.0 with perchloric acid) and 30% methanol, and detected at its maximum of 415nm. The response was linear over the 1.0x10(-7) to 8.0x10(-5)M concentration range with a detection limit of 5.0x10(-8)M and a relative standard deviation of 1.0% at the 5x10(-6)M level. The analysis was free from common ions except iron, which could be successfully screened by 1,10-phenanthroline. This method has been employed to the determination of Al in environmental and biological samples. Moreover, direct speciation of labile monomeric Al, the toxic form of Al, in natural water by the present technique was explored. The coordination ratio of Al complex with quercetin was also elucidated by HPLC combined with molar ratio method. Only a 1:1 complex was formed. Because quercetin exists in body, a preliminary thinking of in vivo determination of Al is provided in this study.