A fixed bed reactor under argon flow was used to pyrolyse small samples of polypropylene (PP) and atactic polypropylene (APP). A special gas-phase sampling technique was used to determine the composition of products eluted from the reactor as a function of temperature and time. Capillary gas chromatography was used to determine the total volatile product evolution rate. The maximum volatile product evolution temperature was 420 C for APP and 425 C for PP. The recovery of carbon as an organic volatile product was determined and pyrolysis products were classified as a carbon number. The pyrolysis products were also identified with gas chromatography/mass spectrometry (GC/MS). Polypropylene (PP) and atactic polypropylene (APP) decomposed into a large number of aliphatic compounds without a residue. The variety of products was more complex than from polyethylene degradation. Due to the branched structure of PP and APP, also branched isomers are formed. 96 wt.% of carbon in PP and 97 wt.% of carbon in APP was converted to volatile organic compounds such as dienes, alkanes, and alkenes. Major compounds are for instance C compounds, like 2-methyl-4-octene, 2-methyl-2-octene, 2,6-dimethyl-2,4-heptadiene, 2,4-dimethyl-1-heptene, 2-methyl-1-octene. The thermal degradation of both PP and APP were investigated under non-isothermal conditions. The weight loss data have been analyzed by Flynn and Wall methods. The activation energies for overall degradation of PP and APP were determined.