The impact behavior of the in situ TiB2/Al composite was investigated at temperatures varying from -50 to 200 A degrees C. The effects of the reinforcement, heat treatment as well as temperature on the impact toughness and failure mechanism were discussed. Results showed that the impact toughness of the composite decreases significantly due to the presence of the stiff TiB2 reinforcements. The precipitations caused by aging play the same role as TiB2 reinforcements, which constrain the deformation of the matrix and reduce the impact toughness. The TiB2/Al composite is more endurable in suffering the impact load at subzero and high temperatures compared to that at room temperature. The fractography of the TiB2/Al composite is a cleavage-and-dimple morphology. The eutectic silicon is the preferred site for catastrophic cracking. There is no cracking in the in situ TiB2 reinforcement because of the small size and near spherical shape. However, the "pulled-out" failure occurs for the TiB2 reinforcement, which is due to the relative weaker interfacial strength than the strength of reinforcement.