A sensitive method for the simultaneous determination of Cr(III) and Cr(VI) using in-capillary reaction capillary electrophoresis separation and chemiluminescence detection was developed. The procedures were designed as follows: The sample, hydrochloric acid and sodium hydrogen sulfite solution segments were injected sequentially into the capillary. The reaction of Cr(VI) reduced to Cr(III) by HSO3- occurred inside the capillary after applying the running voltage. According to the migration time difference of both Cr(III) ions moving towards to the cathode (detection end), they could be separated and determined. The limits of detection for chromium(III) and chromium(VI) (S/N = 3) were 6.010-13 mol/L (12 zmol) and 1.910-11 mol/L (380 zmol), respectively. A sensitive method for the simultaneous determination of Cr (III) and Cr (VI) using in-capillary reaction capillary electrophoresis separation and chemiluminescence detection was developed. The procedures were designed as follows: The sample, hydrochloric acid and sodium hydrogen sulfite solution segments were The reaction of Cr (VI) reduced to Cr (III) by HSO3- occurred inside the capillary after applying the running voltage. According to the migration time difference of both Cr (III) ions moving towards to cathode The limits of detection for chromium (III) and chromium (VI) (S / N = 3) were 6.010-13 mol / L (12 zmol) and 1.910-11 mol / L (380 zmol), respectively.