PURPOSE: To provide the titled compsn. giving moldings which have excellent dimentional stability and good surface gloss and do not form sinkmarks, by adding an inorg. filler and an azodicarboxylic acid amide blowing agent to polypropylene and blending two specified kinds of compds. with the mixture.

CONSTITUTION: 5W50wt% inorg. filler such as calcium carbonate or talc and 0.1W2wt% blowing agent are added to polypropylene. 0.05W1wt% 1.3,2.4-di(alkylbenzylidene) sorbitol (A) and 0.05W1wt% aluminum di-p-t-butylbenzoate (B) are added to the resultant compsn., each amount being based on that of said compsn. The blending ratio of A/(A+B)=33W67wt% is preferred.