In recent years incinerated municipal solid waste has been disposed of in landfill sites near the coastal area in Japan where the underlying marine clay deposits are expected to serve as a natural clay barrier. In this study, marine clay from Japan is examined for the effects of salt on sorption of lead using column leaching tests with deionized water, sea water, and bottom ash leachate spiked with 100 mg/L lead as permeants, and then selective sequential extraction (SSE) was employed to assess the retention mechanism of lead onto marine clay. Lead concentration in the effluent was less than 5 MG/L throughout the column leaching tests with the deionized water, whereas it exceeded Pb concentration in influent below one pore volume leaching for the sea water. Lead in pore water accumulated in the top layer of the column soil for the deionized water whereas it was distributed throughout the depth for the sea water and ash leachate. The SSE indicated that carbonate, exchangeable, and hydroxides phases are predominant for Pb retention.