On the basis of viscometry technique a novel method was developed to determine the induction period for polymer thermal oxidation (tau i). Natural rubber films from Manihot glaziovii degradated at 90 degrees C were used as a model. (M) over bar v values were calculated by using the equation : [eta] = 1.9 x 10(-4) (M) over bar v(0.745) in toluene at 30 degrees C. A random chain scission process was applied. A plot of lnN (N is the number of broken bonds, C=C in case of rubber) versus time of heating shows two lines. The first indicates no degradation (lnN = lnNo, to t less than or equal to tau i) while the second represents the real kinetics of the process (lnN = lnNo - k (t - tau i), to t greater than or equal to tau i). The intersection of these lines is the induction period of thermal oxidation. The effect of a protective agent, carnauba wax, was tested. The resolution of the method is comparable to that of chemiluminescence and is superior to that of IR and DSC.