The kinetics of the early stages of thermal degradation below 1% dehydrochlorination of emulsion-polymerized poly(vinylidene chloride) (PVDC) is studied by the variation of the pH value of potassium hydroxide aqueous solution between 160 and 190 degrees C in the presence of air and other gas streams. The results turned out that the thermal degradation of PVDC can be divided into three stages, which correspond to an induction period, a period with conversion below 0.1% dehydrochlorination, and that with conversion ranging from 0.1 to 1%. For the induction stage, the induction time depends upon the types of environment gas and degradation temperature. Both of the second and the third stages are zero-order reactions, which also result in the discoloration and crosslinking of the neat polymer. The average apparent activational energy of the zero-order degradation reaction was about 21 kcal/mol, which is independent of the types of environment gas. The whole degrading kinetics data can be well explained by the mechanism of a free-radical-induced dehydrochlorination. The viscosity of the degraded sample increases rapidly with degradation and becomes insoluble in regular solvents.