The state of egg yolk phosphatidylcholine (EPC) vesicles adsorbed on solid surfaces was evaluated by studying the aggregation behavior of the latex or silica particles with vesicles and the adsorption behavior of the vesicles on the surface. The aggregation behavior of latex and silica particle dispersions after adding EPC vesicles was studied using a dynamic light scattering method and optical microscopy. The adsorption of EPC vesicles on the solid particles was conducted by electrostatic attraction in a 10(-4) M LaCl3 aqueous solution. The amount of EPC adsorbed was determined by the depletion of EPC in the bulk solution. The state of EPC adsorbed was estimated by comparing the experimental and calculated results of the amount of EPC adsorbed. It was concluded that the EPC vesicles existed on the solid particle surface as a particle state, but not a bilayer membrane, and a "particle bridge" aggregation occurred at certain concentrations.