This investigation proposes a new method for the determination of lead and cadmium ions in contaminated waters by dithizone-modified cellulose acetate polymeric membranes. This method is precise, cost-effective and eco-friendly. Quantitation of analytes was performed by flame atomic absorption spectrometry technique. The method is based on the retention of Pb and Cd by an adsorbent which its effective component is dithizone, a strong chelating ligand with lead and cadmium ions. Some important parameters affecting the analytical performance of the method such as pH, flow rate of the sample solution and eluent; concentration and volume of the eluent were optimized. Maximum adsorption capacities of adsorbent were 787 mg g-1 for Pb(II) and 195 mg g-1 for Cd(II). LODs (3σb) of 0.012 mg L-1 (Pb) and 0.001 mg L-1 (Cd) were obtained. Linear range of calibration curves were 0.044-1.047 and 0.006-0.113 mg L-1 for lead and cadmium ions, respectively. RSD% of the method in optimized conditions was below than 5% for lead (0.25 mg L-1) and cadmium (0.025 mg L-1) ions. Enrichment factors of the method were more than 19 and 17 for Pb and Cd ions, respectively.