A method was developed for the preconcentration of copper, nickel and cadmium in water samples, prior to their determination by FAAS, using the Zn- piperazinedithiocarbamate complex (ZnPDC) loaded on activated carbon. In this method, Cu, Ni and Cd in liquid phase quantitatively replaced zinc on a ZnPDC-activated carbon solid phase. Afterwards, the metals on the solid phase were easily eluted by Hg (II) solution into aqueous phase, and were measured by FAAS. The optimum experimental parameters such as pH, sample volume, and effect of matrix ions for the preconcentration of the metals were investigated. The range of linearity 0-6, 0-5, 0-3 μgml-1, correlation coefficient 0.998,0.996,0.999, detection limits 15.7, 2325, 11.8 ngml-1 and determination limits 136, 179, 98 ngml-1 in final Hg(II) solution were obtained for Cu, Ni and Cd, respectively. The proposed method has been employed for the determination of Cu, Ni and Cd in various standard metal alloys and natural water samples.