Titanium matrix composites reinforced with TiB whiskers were in situ synthesized by spark plasma sintering (SPS) at a temperature range of 1173–1473 K, using a mixture of 6.2 mass% TiB₂, 4.1 mass% Ti, and 89.7 mass% Ti6Al4V powders. The in-situ synthesis mechanism and the effect of sintering temperature on the sintering microstructure were investigated. The results show that an increase of the sintering temperature causes the relative densities of the composites to increase and the reaction between Ti and TiB₂ to be more complete. Nano-sized TiB reinforcements with a diameter of around 80 nm and fine-grained matrix with an average grain size of 12 µm are obtained after SPSed at 1373 K. Clean and perfect TiB/matrix interfaces without debonding or cracks are obtained during SPS process. Low sintering temperature and short sintering time are believed to be the main reasons for the improved fine-grained microstructure.