Abstract: Influence of surface treatment with B4C on the microstructure and properties of Ti-6Al-4V was studied.The Ti-6Al-4V was treated at 800℃ and 1000℃ for 20h,respectively,via the process of solid diffusion.There was a continuous compound layer mainly consisted of TiC,TiB and TiB2 on the surface of substrate.But in the deep of substrate,there was a diffusion layer in which many lath shape or equiaxed particulates distributed along the grain boundaries.Consequently,the microhardness of the surface of Ti-6Al-4V was increased tremendously,and it formed an excellent gradient with higher microhardness in the outer and lower in the inner.The SEM micrographs indicated that the substrate became more brittle if treated at a higher temperature.