TiB2/TiC nanocomposite powder was synthesized by ball milling the industrial grade Ti powder and B4C powder. The results show that the milling atmosphere plays a crucial role in the synthesis of TiB2/TiC. After 5 h milling under an appropriate argon protection, a solid state reaction between Ti and B4C occurs resulting in the formation of TiB2/TiC phases. With increasing of the milling time, the crystal size of synthesized TiC is decreased to about 10 nm while the crystal size of TiB2 is slightly larger. When the air is introduced in the milling process, a large amount of TiN and TiO will occur in the milled product.