A suitable capillary electrophoresis (CE) method was developed and validated for sulfate anion determination in effervescent tablets of Digedryl. The large excess of other ions in the matrix (i.e. excipients) constituted the main difficulty of this method's development. So an original analytical procedure for both the conditioning and rinsing of the capillary was purposed including a running electrolyte constituted by boric acid 20 mM and hexamethonium dibromide 0.75 mM at pH 8.00. Separation was carried out on a 60.2 cm (50 cm to the detector) x 0.75 microm i.d. fused-silica capillary at a potential of -29 kV and 35 degrees C. Indirect UV detection was performed at a wavelength of 254 nm using a background electrolyte containing potassium chromate. Nitrate anion was used as an internal standard for quantification. This CE method was validated in terms of selectivity, linearity, accuracy and precision.