PURPOSE: To make it possible to mold a specified cyanoaryl ether polymer without detriment to its properties such as mechanical strengths by improving its heat stability, by mixing said polymer with a specified amount of zeolite as a heat stabilizer.

CONSTITUTION: 0.1W10wt.% zeolite (e.g., zeolite A) as a heat stabilizer is added to a cyanoaryl ether polymer comprising repeating units of formula I (wherein Ar is phenylene, biphenylene or naphthylene) to obtain the purpose heat-stable cyanoaryl ether polymer composition. Said cyanoaryl ether polymer of formula I can be obtained by polycondensing a dihalogenobenzonitrile of formula II (wherein X and X' are each a halogen), e.g., 2,6-dichlorobenzonitrile, with a dihydroxyaryl compound of formula III, e.g., hydroquinone.