PURPOSE: To provide a method for easily and efficiently obtaining a stereoregular polymer having high syndiotacticity, by preparing a suspension with a vinyl aromatic monomer and a nonsolvent for this monomer and the formed polymer, and then bringing it into contact with a coordination catalyst to polymerize the monomer.

CONSTITUTION: The stereoregular polymer having high syndiotaciticity is provided by mixing a vinyl aromatic monomer (e.g. styrene, etc.) with an inactive liquid [e.g. perfluoro(methylsiloxane), etc.], which is nonsolvent for this monomer and the formed polymer to form a suspension, adding to the mixture a coordination catalyst which is prepared by cooling a mixture containing methylaminoxane, triisobutyl aluminum, etc., to -5°C and adding monocyclopentadienyl titaniumtriphenoxide, etc., and contacting the suspended monomer with the coordination catalyst under the polymerization condition to polymerize the monomer.