Ti6Al4V alloy specimens were put into a vacuum furnace for hydrogen-free carburization. The phases, microstructure, composition and hardness of the carburized coating were analyzed by XRD, SEM, EDS and HV hardness tester, respectively. Results show that after carburization TiC phase appears in the coating, but no hybrids or H-containing phase are observed. The total carburized coating is composed of accreted layer, carburized layer and diffusion layer. The accreted layer containing Ti, Al and V elements inhibits the permeance of carbon. The carburized layer is composed of dense layer I and equiaxed-crystal-shaped layer II. The diffusion layer has a little carbon, so it is only a carburization-influenced zone. The HV microhardness of the carburized coating has a gradient change. The change of hardness reflects the change of carbon content. The hardened layer is about 900 μm thick