The interaction between lecithin liposomes and acid clay was investigated to clarify the mechanism for liposome adsorption to the clay. It was found that the multilamellar vesicular structure of the liposomes was broken as a result of primary adsorption. The acid clay particles aggregated and were eventually covered by the lecithin layer structure. In the case of kaolin, on the other hand, the liposomes were weakly adsorbed to the clay and maintained the vesicular structure. The amount of primary adsorption to the clay surface, which was estimated from the adsorption isotherm, was more for acid clay than for kaolin, and the total amount adsorbed to the acid clay was also more than to kaolin. This result can be explained by the much higher density of the negative charge on the acid clay surface than that for kaolin. The liposomes are therefore considered to be adsorbed to the acid clay mainly by the choline positive charge residing at the end of the lecithin molecule, although this is of no net charge as a whole.