The present invention provides a process for producing a crystal nucleator composition comprising; a first step pulverizing 95% by mass or more of a crystal nucleator ingredient containing one or two or more kinds of specific compounds to a primary particle diameter of 0.8 .mu.m or smaller with a dry medium-stirring type pulverizer; and a second step mixing and pulverizing the pulverized crystal nucleator ingredient obtained in the previous step and a metal aliphatic carboxylate ingredient containing one or two or more kinds of specific metal aliphatic carboxylates. Also provided is a crystalline polymer composition comprising a crystal nucleator composition obtained by the production process