The phenomenon of interfacial convection induced by mass transfer was investigated in aceton-toluene-water systems. In particular, the Rayleigh effects were examined with the change in vertical direction of mass transfer by inserting a porous membrane between two phases. The convective flow patterns were visualized by the optical technique of shadowgraph and the periods of eddy generation were measured by a specially disigned photosensitive detector. In the present experiments, the interfacial-tension effects were effectively suppressed by the membrane. The flow patterns of interfacial convection caused by the density gradient effect were shown to be the type of thermals, which were generated periodically from the interface. The generation period and the size of eddies decreased with increase in the concentration driving force. It was found that the rate of solute transfer accompanied by buoyancy-driven convection inreased 2-4 times as high as that of the pure molecular diffusion for 5×10⁷<Ra<1.5×10¹¹.