PURPOSE: The titled accelerator, consisting of an alkaline earth metallic salt of an aromatic sulfonic acid, capable of remarkably increasing the crystallization rate, advancing the crystallization uniformly even in injection molding at a low mold temperature without coloring and reducing the injection molding cycle.

CONSTITUTION: A crystallization accelerator for a polyester consisting of an alkali metallic or alkaline earth metallic salt of an aromatic sulfonic acid expressed by the formula{H-(OCHR1-CHR2)lO}mAr-(SO3H)n (Ar is aromatic ring; R1 and R2 are H or 1W4C alkyl; l is an integre 1W10; m and n are 1 or 2), preferably sodium 4-(2-hydroxyethoxy)benzenesulfonate. 0.05W5.0pts.wt. accelerator is powerfully melt keaded with 100pts.wt. polyester. The accelerator may be added to the material before the polymerization of the polyester is completed. In this case, the accelerator may be used in an amount of 0.1W5mol% based on the total acidic component.