A water-fine particle suspension with a uniform initial temperature and concentration in a rectangular cell is heated from a central part of the horizontal bottom wall and temperatures at both the vertical side walls of the cell are kept at the initial temperature. This transient natural convection is experimentally studied. During the fall of particles, the suspension forms layers. Concentration of particles, average diameters of particles, temperatures in each layer and time-dependent heat transfer coefficients on the heated bottom wall are measured. The mechanisms of formation and vanishment of the layers are clarified.