The determination of EDTA in mayonnaise by on-line coupled capillary isotachophoresis and capillary zone electrophoresis (CITP-CZE) is described. EDTA was determined as a negatively charged complex with Fe(III) using photometric detection at 254 nm with the help of column coupling isotachophoregraph. Two operational electrolyte systems at different pH were employed. A 10 mM HCl / 20 mM L-histidine / 0.1% hydroxypropylmethylcellulose (HPMC), pH 6, 5 mM morpholinoethanesulphonic acid (MES), and 25 mM MES / 10 mM BisTris propane, pH 6.4, served as leading, terminating, and background electrolytes, respectively. Leading, terminating, and background electrolyte of the second system consisted of 10 mM HCl / 14 mM balanine (BALA) / 0.1% HPMC (pH 3.3), 5 mM acetic acid, and 100 mM acetic acid / 20 mM BALA (pH 3.7), respectively. Only a water extraction of mayonnaise (2 g/100 ml) is necessary prior to CITP-CZE analysis. The detection limit of EDTA was 3 mg/kg; repeatability better than 5% and recovery of 37 mg/kg EDTA addition higher than 95%. Besides the determination of EDTA in mayonnaise the analysis of EDTA-Fe(III) complex can also be utilized for the determination of Fe(III).