Abstract: In a acetate buffer solution of pH 7.0,a blue-green ternary complex,was formed by the reaction of Al(Ⅲ),with polyethylenedioxy octylbenzene (OP) and chrome azurol S (CAS),having the absorption maximum at the wavelength of 610 nm.Beer′s law was kept in the range within 0.4 mg· L-1.Main species of aluminum (active Al3+ ion,total active Al3+ ion,organic aluminum and water insoluble aluminum) were separated as follows: (1) active Al3+ (wc) was separated from the water or tea sample on cation ion-exchange resin column,and Al3+ in the eluate was determined by CAS-spectrophotometry as described;(2) another portion of the sample was treated with HNO3,evaporated to dryness and taken up the residue with dil.HCl.Total active Al3+ (wt) was determined as above in the solution obtained;(3) amount of organic aluminum was obtained by the difference of wt and wc (wt-wc);(4) water insoluble aluminum was filtered from the sample solution with 0.45 μm filtering membrane,which was treated with HNO3 and HCl,and its content of aluminum determined as mentioned above.