A reactive acrylic resin micro-particle comprising a particulate body resin and a number of linear segments attached to said body resin and extending outwardly therefrom, said particulate body resin being composed of an internally gellated acrylic resin and having a mean grain diameter of 0.01 to 20 .mu. and said linear segments each being composed of a linear carbon chain of 1 to 100 carbon atoms, which may be interrupted by an oxygen, sulfur or nitrogen atom, which is connected at one end to said particulated body resin through a urethane, acyl urethane, urea or acyl urea bond and possessed of at the other end an ethylenically unsaturated bond. The invention also includes the preparation of said microparticles and a curable acrylic composition containing said microparticles, at least one polymerizable monomer or oligomer and a polymerization initiator.