Polycarbosilane (PCS) with highly crosslinked structure and high surface area was synthesized by the polycondensation reaction between trimethoxyvinylsilane and trichloromethylsilane. The reaction was conducted in the presence of sodium metal. Manganese ion was supported on PCS. The immobilization of transition metal ions to polymer support leads to a number of advantages over homogeneous catalyst, viz easy product recovery, increased selectivity, etc. The catalytic activity of PCS supported manganese ion was studied by considering three-component Mannich reaction. Reaction with diverse sets of aldehydes, amines, and ketones was examined. PCS-supported manganese ion catalyst has been prepared for the first time and used successfully in Mannich reaction. (C) 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2012