An anthraquinone (AQ) improved Na-montmorillonite nanoparticles (nano-SWy-2) chemically modified electrode (CME) has been developed for the simultaneous determination of trace levels of cadmium (II) and lead (II) by differential pulse anodic stripping voltammetry (DPASV). This method is based on a non-electrolytic preconcentration via ion exchange model, followed by an accumulation period via the complex formation in the reduction stage at -1.2V, and then by an anodic stripping process. The mechanism of this design was proposed and the analytical performance was evaluated with several variables. Under the optimized working conditions, the detection limit was 3 and 1nM for Cd(2+) and Pb(2+), respectively. The calibration graphs were linear in the concentration ranges of 8x10(-9) to 1x10(-6)molL(-1) (Cd(2+)) and of 2x10(-9) to 1x10(-6)molL(-1) (Pb(2+)). Many inorganic species did not interfere with the assay significantly; the high sensitivity, selectivity, and stability of this nano-SWy-2-AQ CME were demonstrated. The applications for the detection of trace levels of Cd(2+) and Pb(2+) in milk powder and lake water samples indicate that it is an economical and potent method.