The present invention discloses a novel toughener selected from the group of polyurea, polyurethane and poly(urea-urethane) using a facile synthesis method. The toughener forms thick-interface particles, and creates an effective toughness improvement for epoxy resin. Different from the conventional epoxy/rubber composite or epoxy/thermoplastic composite, the epoxy/polyurea, epoxy/polyurethane, or epoxy/poly(urea-urethane) composite shows Newtonian rheological behaviour, a convenient property for processing. The unique feature of the toughener according to the present invention is that toughness can be significantly improved at low toughener content without losing other desirable properties.