The present invention provides a supported catalyst comprising (A) a polymer (B) a supporter, (C) a transition metal compound, and optionally (D) (a) a compound which can form an ionic complex by the reaction with the transition metal compound or (b) a specific oxygen-containing compound, and (E) an alkylaluminum compound. The supported catalyst according to present invention, which has a high activity, can be used for preparing a styrenic polymer with a high syndiotacticity. The supported catalyst can be used in combination with a cocatalyst, preferably an alkyl aluminoxane.