The extraction equilibria of chromium(VI) from sulfuric acid solutions with tri-n-octylphosphine oxide (TOPO) dissolved in kerosene at 25 degrees C have been studied. The possible complexes of chromium(VI) with TOPO in organic phase and extraction constants were determined by best fitting the distribution coefficient expression of Cr(VI) with experimental data using the Rosenbrock method. The extraction reactions, including the equilibria among seven species in aqueous phase (H2CrO4, HCrO4-, HCr2O7-, Cr2O72-, CrSO72-, HSO4-and SO42-) and five possible complexes in organic phase (H2CrO4.(TOPO), H2Cr2O7.(TOPO)(3), H2CrSO7.(TOPO)(3), H2SO4.(TOPO)(2) and (H2SO4)(2).(TOPO)(2)) were proposed. The influence of initial sulfuric acid concentration on the fraction of extracted complexes and on the distribution coefficients of Cr(VI) is discussed. This result was helpful for the clarification of the extraction reactions of Cr(VI).