Polypyrrole films doped with dodecylsulfate （PPy/DS-）were synthesized on platinum substrates by electrochemical polymerization and the film-electrode systems were investigated as electrochemically switched ion exchange materials.Electrochemical quartz crystal microbalance （EQCM）technique was used to investigate the polymerization mechanism of the PPy/DS- film.Combined with Cyclic Voltammetry （CV）and X-ray photoelectron （XPS），the electrochemical behavior and ion loading/unloading mechanism of PPy/DS- film electrodes were also investigated in electrolytes of alkali-metals and alkaline-earth metals.Experimental results indicated that PPy/DS- film had good electroactivity.The oxidation and reduction process of PPy/DS- film were accompanied by cation exchange and anion exchange simultaneously，and cation or anion exchange could be performed singly by controlling scan potential.In CsNO3 solution，only Cs+ could be exchanged when the thin film was scanning between -1.05 V and 0.14 V.The cycle life in alkali-metals nitrates was better than that in alkaline-earth metals nitrates，especially in CsN