PURPOSE: To obtain a resin body with improved toughness by incorporating a reactive modifier into a thermoplastic resin component containing a cyanate ester and/or a maleimide thermosetting resin and a polyarylsulfone or polyimide.

CONSTITUTION: A resin body comprises 1-98 wt.% of a thermosetting resin selected from composition A, 1-98 wt.% of a thermosetting resin selected from either or both of composition B and composition C, 1-98 wt.% of a reactive modifier, 0-5 wt.% of a catalyst, and 0-5 wt.% of a radical quencher, wherein the thermosetting resins comprise a di/polyisocyanate ester and/or maleimide and/or an oligomer and/or combinations of them, composition A comprises a cyanate ester of formula I, composition B comprises a polyimide of formula II, and composition C is a polyarylsulfone comprising repeating units of ether and/or thioether bonds, formula II, formula IV and/or Pha, in which Ph represents phenylene and (a) represents about 0-2.