To obtain the subject polymer high in rigidity and thermal resistance by polymerizing propylene under controlled conditions in the presence of a solid titanium compound polymerization catalyst consisting of a specific solid titanium compound, an organoaluminum compound and a specific organosilicon compound.

This highly crystalline polypropylene is produced by polymerizing propylene under controlled conditions in the presence of a solid titanium compound polymerization catalyst consisting of (A) a solid titanium compound essentially containing magnesium, tetravalent titanium, a halogen and an electron-donor, (B) an organoaluminum compound and (C) an organosilicon compound of the formula R1R2Si(OR3)2 (R1 to R3 are each a 1-20C hydrocarbon group, wherein R1 and/or R2 is a linear hydrocarbon group with a tertiary carbon directly bound to Si, or a cyclic hydrocarbon group with a secondary carbon directly bound to Si), wherein the propylene is polymerized by controlling the polymerization conditions so that the resultant polypropylene has Si and Cl concentrations of ≤10ppm, respectively, and isotactic pentad fraction of ≥0.97.