Abstract: In this paper a mono-molecular model of the end-peeling reaction of atactic polypropylene (APP) was proposed, based on the experimental results, such as iodine value, viscosity and molecular weight distribution of raw material and the products of pyrolysis of APP.An equation of the zero-order reaction of polymer pyrolysis was derived: dm_p/dt=K₀m₀. Another equation for the calculation of the velocity of the mono-molecular first-order pyrolysis reaction, which was considered to be taken place at the final stage of peeling, was also derived: dm_p/dt=k₁m (where k₁=2k₀).