In-situ synthesized (TiB + La2O3)/Ti-6Al-4V titanium matrix composites (TMCs) were successfully processed by equal-channel angular pressing (ECAP) at the temperature of 600 °C, 700 °C, 800 °C and 900 °C. The deformed microstructure characteristic indicated that the grains and hard reinforcements were severely influenced by the ECAP temperature. Ultrafine-grained structure partially formed during the severe plastic deformation (SPD) process. Plenty of dislocation pile-ups, tangling and cell structures of about 500 nm can be observed in the matrix processed at 600 °C or 700 °C. Many new ultrafine grains (100–500 nm) with clear grain boundaries have formed due to the dynamic recrystallization in the matrix processed at 800 °C or 900 °C. The most remarkable grain refinement occurred at 900 °C, and the average thickness of lamellar α phases were reduced to less than 1 μm, compared with the initial average thickness of 2.1 μm. As for the reinforcements, TiB whiskers were broken both in radial and axial direction. The average aspect ratio decreased as the ECAP temperature increased due to the different load-bearing modes in the TMCs. Moreover, high density dislocation tangling and pile-ups around the TiB whiskers tended to form ultrafine grains.