A new and simple method for the simultaneous determination of cations and anions by microchip electrophoresis with capacitively coupled contactless conductivity detection (ME-(CD)-D-4) is described. The best analytical performance was found by applying a sinusoidal wave with 800 kHz frequency and 20 V,, amplitude. An optimized background electrolyte (BGE) composed of 20 mM His/MES and 0.01 mM CTAB was chosen for the simultaneous analysis. Samples containing K+, Na+, and Li+ as the cations and Cl-, F- and PO43- as anions were analyzed simultaneously in a single run (within 3 min). The reproducibility obtained by the method was compared with those obtained in previous studies that had employed simultaneous analysis of anions and cations by ME-(CD)-D-4. The proposed simultaneous determination method is inexpensive, simple, fast, easy to operate, and offers a high degree of integration.