A common casting technique has been applied to fabricate Ti-TiB-TiC in situ composite utilizing the self-propagation high-temperature synthesis (SHS) reaction between Ti and B4C. The microstructure of TiB/Ti interfaces has been investigated by means of scanning electron microscopy (SEM), transmission electron microscopy (TEM) and high-resolution transmission electron microscopy (HREM). The TiB/Ti interfaces are atomically flat, sharp and free from any interfacial phase. TiB is also well bonded with the matrix. The following consistent crystallographic relationships between TiB and Ti have been observed by HREM, namely, [010](TiB) // [01 (1) over bar0](Ti), (100)(TiB) // ((2) over bar 110)(Ti), (001)(TiB) // (0002)(Ti), (10 (1) over bar)(TiB) // (4 (2) over bar(2) over bar1)(Ti) and [001](TiB) // [01 (1) over bar0](Ti), (010)(TiB) // ((2) over bar 110)(Ti), (200)(TiB) // (0002)Ti. The formation mechanism of TiB/Ti interfaces has been analyzed by solidification theory.