PURPOSE: To crystallize by bringing an amorphous, solvent-resistant, high temperature type polymer into a specific organic compound at a specific temperature for a specific time.

CONSTITUTION: A pre-molded product containing an amorphous poly(etheretherketone)type polymer [e.g. a poly(etheretherketone), poly(etherketone), etc.] is brought into contact with an organic compound having a mol.wt. of 160-320 daltons (e.g. fluoranthene, m-terphenyl, etc.) for 0.10-150 hours, preferably 24-100 hours to crystallize.