Department of Chemistry, University of Burdwan. Golapbag, Burdwan-713 104, West Bengal. India E-mail : arabindakdas@rediffmail.com; debasishbanerjebu@yahoo.com Fax : 91-342-2557938 Manuscript received 26 October 2005, revised 1 February 2006, accepted 7 February 2006 Separation and preconcentration of two forms of chromium viz. CrIII and CrVI in natural ,water was carried out applying a resin containing xanthine moiety anchored onto polystyrene-divinylbenzene (8%) by azo (-N=N-) function. The maximum exchange capacity of CrIII was found to be 0.6718 mmol g-1 at pH 6.5 and that for CrVI was 1.1324 mmol g-1 at pH 1.0. The sorption of both CrIII and CrVI onto resin follows a second order kinetics with rate constant values of 0.0-'7 and 0.410 mmol-1 min-1 for CrIII and CrVI respectively. The two species CrIII and CrVI arceluted completely by 3 M aud 4 M HCl respectively. The detection limits of 4.3 and 5.1 µg ml-1 for CrIII and CrVI were achieved. The optimum llow rate, sample breakthrough volume of column operation for CrIII and CrVI species were found to be 1.2 ml min-1 and 3000 ml respectively. Finally the developed method using this resin was applied for determination of these two species in synthetic binary mixtures, natural water samples and validated comparing with results using previously developed method.