Both theoretical and experimental drying indicate that it is necessary to know the kinetics of drying of various materials. It has been generally accepted that in the first period of drying the process is analogous to evaporation from a free liquid surface, and thusthe drying agent parameters have a significant influence. There is, however, lack of a uniform opinion on the mechanism of drying in the falling drying rate period, although many studies have been devoted to these problems. Since it appeared to be very difficult tosolve analytically the differential equations of the transport phenomena, an attempt is made a t developing approximate methods for a mathematical description of the drying kinetics. The paper presents a new mathematical method of convection drying in the falling drying rate period. Applying the principles of variational calculus, the generalized equations of the temperature and drying curves for the falling drying rate period are obtained.