Drying rates of finely powdered aluminum soaps and diatomaceous silicas were determined in a tray dryer. The weight of solid on the tray was automatically recorded. As expected for fine powders, plots of drying rate against moisture content were concave downward. The data were correlated by equations of the form N = aXG0.625 where N is the drying rate in lb./(hr.) (sq.ft.) and XG is the free moisture content in lb. of water per lb. of dry solid. A straight line was obtained by plotting log a for aluminum stearate against the reciprocal of absolute temperature and a similar relationship was assumed to hold for the other materials which were dried at two temperatures only. Intercepts of the temperature plots seemed to depend upon bulk density or average particle size but no general correlation was possible.