The cooling function (kappa) in Ozawa model was investigated through theoretic analysis and experimental method. Different from the fact accepted by researchers over past decades that kappa(T) depends only on the crystallization temperature (T) and consequently the parameters for nonisothermal crystallization kinetics could be obtained by plotting ln[- ln(1 - X(T))] versus In lambda at a given T, we found that kappa at a given T was also dependent on onset temperature (T-0) of crystallization process. Because T-0 varies with cooling rate (lambda) in nonisothermal crystallization, we conclude that K is a binary function of T and lambda, which was validated by our kinetic data from differential scanning calorimetry measurement in a wide lambda range from 1 to 80 degrees C/min. It is suggested that the conventional method for calculating kinetic parameters based on Ozawa model, by plotting In[- ln(1 - X(T))] versus lambda, might not be exact for nonisothermal crystallization. (c) 2006 Wiley Periodicals, Inc.