An improved rate equation was proposed to investigate nonisothermal crystallization kinetics. The reaction model, activation energy and pre-exponential factor were determined by using the multivariate linear regression method. A particular form of the effective activation energy was derived from the improved rate equation, and experimental data reported in previous studies were used to validate the reliability of the proposed rate equation. Results indicate that the values of effective activation energy obtained from the improved rate equation are similar to those obtained from the isoconversional method. When the improved rate equation is used to fit the crystallization rates under different cooling or heating rates simultaneously, the correlation coefficient is between 0.982 and 0.998, which indicates that the proposed rate equation is capable of describing the variation of the crystallization rates during nonisothermal processes.