1. The dependence of the polymer crystallization rates on temperature is considered on the basis of the general theory of crystallization kinetics for supercooled liquids. The coefficients in the equations relating the crystallization half time, τ½, to the degree of supercooling are calculated for natural rubber. 2. An approximate expression is obtained which relates the equilibrium melting temperature of deformed rubber with the mechanical stress applied when crystallization starts. 3. The acceleration of crystallization which is induced by deformation is shown to be basically associated with an increase of the equilibrium melting temperature. 4. The possibility of calculating the crystallization rate at all temperatures and stresses from the results of a small number of experiments is established.