A membrane-type adsorbent of spinel-type manganese oxide was prepared by a solvent exchange method using poly(vinyl chloride) (PVC) as a binder. PVC was dissolved in, N,N-dimethylformamide (DMF) solution, after which spinel-type lithium manganese oxide was mixed with the DMF solution. The suspension was spread into a thin film, and immersed in water to solidify the PVC. The membra ne was treated with an HCl solution to extract lithium, resulting in a membrane-type adsorbent. The preparation conditions were studied by changing the initial PVC concentration versus DMF and lithium manganese oxide content.. The membrane thickness, manganese oxide content, and tensile and abrasion strengths were measured for each membrane. A new type of adsorption cell was designed for obtaining a parallel seawater flow along the membrane-type adsorbents. The lithium adsorption experiment was earned out using natural,, seawater at a linear velocity of 1.25 cm/min. Placing the membrane between spacers was found to be effective in raising the lithium adsorption rate., The adsorption rate, depended on the preparation conditions. The membrane prepared from an initial PVC concentration of 8%, and a PVC additive content of 20% is optimum for the adsorption of lithium in seawater. The adsorbed lithium could be easily eluted by treating an, HCl solution.