PURPOSE: To obtain the subject composition comprising specific propylene polymer and a thioether stabilizer in a specified ratio, excellent in thermal stability, and useful for sheets, etc.

CONSTITUTION: This composition comprises (A) 100 pts.wt. of propylene polymer, (B) 0.001-10 pts.wt. of a thioether stabilizer such as dilaurylthiodipropionate, and further preferably (C) 0.001-10 pts.wt. of one or more compounds selected from a hindered amine stabilizer and a higher fatty acid metal salt. The propylene polymer A has a MFR of 0.1-500g/10min, a stereoregularity index [M5] value of 0.970-0.995 determined by an equation I from the absorption strengths of Pmmmm, Pw in the 13C-NMR spectrum of boiling heptane-insoluble components, a stereoregularity index [M3] value of 0.0020-0.0050 determined by an equation II from the absorption strengths of Pmmrm, Pmrmr, Pmrrr, Prmrr, Prmmr, Prrrr, Pw in the 13C-NMR spectrum of boiling heptane-insoluble components, and a boiling heptane-insoluble component crystallinity of ≥60%.