Ultrafine TiB2 particle (20 vol%) reinforced copper matrix composites were fabricated in-situ from Ti-B-Cu system through exothermic dispersion synthesis (XD). The reaction mechanism and mechanical properties of the composites were studied. It was found that when the reaction system was heated to 1373 K, Cu reacted with Ti to form the transient phase Cu4Ti, which continued to react with B to form ultrafine TiB2 particles as reinforcement agents. The apparent activation energy for these two reactions were calculated and found to be 453.7 KJ/mol and 1139.3 KJ/mol, respectively. Ultrafine TiB2 particles with the size of mostly 100 nm-500 nm were seen to distribute uniformly throughout the copper matrix. The ultimate tensile strength was measured and found to be 318 MPa, representing a 45% increase over pure copper. Moreover, the elongation to failure of the new composites was determined to be 4.4% at room temperature. The tensile fracture surface consists of many fine dimples, suggesting that the failure is of ductile nature. (C)2017 Published by Elsevier B.V.