A dual diffusive gradients in thin film (DGT) device method for in situ fractionation of dissolved inorganic Cr was developed by simultaneously deploying two types of DGT devices with different binding phases in tap water. The concentration of Cr(Ill) in the tap water determined by a DGT device with sodium poly(aspartic acid) (PASP) solution as the binding phase (PASP DOT) was 3.18 mu gL(-1), and the recoveries of the spiked Cr(III) were 97.9%-105.3%; the concentration of Cr(VI) in the tap water determined by a DGT device with poly(quaternary ammonium) salt (PQAS) solution as the binding phase (PQAS DGT) was 2.92 mu gL(-1), and the recoveries of the spiked Cr(VI) were 98.2%-107.7%. The ratios of the total Cr measured by DOT to the total Cr measured by ICP-MS were 102.9%-105.7%.