Mineral fillers are widely used to improve the mechanical properties of polypropylene, but at the same time they may cause some degradation of polymer, especially if the stabilization is insufficient. Two different kinds of silicate minerals, talc and serpentinite, were used as fillers for homo- and copolypropylene, and their influence on mechanical properties and degradation was investigated. The mechanical properties of filled polypropylene were tested at room temperature using tensile and impact tests. GC-MS technique was used to characterize the degradation of compounds. The results revealed differences in the mechanical properties: talc filled polypropylene had higher tensile strength, rigidity and impact strength properties than serpentinite filled. The oxidation stability of filled polypropylene measured by the oven method showed lower values in the case of serpentinite filled polypropylene. In the beginning of pyrolysis there was no significant difference between talc and serpentinite filled polypropylene in the formation of degradation products, as was observed by GC-MS. In a slightly higher temperature and longer incubation time PP-serpentinite compound started to form more small molecular weight degradation products than PP-talc due to stronger catalytical effects of the serpentinite surfaces. The characterization methods used here provided us new information to understand the role of mineral fillers in degradation processes. The results of DSC measurement yielded information on the effects of the filler crystallization and thermal degradation. Talc, for example, was shown to be better nucleation agent than serpentinite for PP.