Ti-6Al-4V alloy is paid the attention from the automotive and aerospace industries because of its outstanding specific strength and corrosion resistance. On the other hand, Ti-6Al-4V alloy has normally poor workability. Therefore, Metal Injection Molding (MIM) process is hoped to be one of the technique to reduce the manufacturing cost. Recently many researches for Ti-6Al-4V compacts by MIM process were reported, however, there are a few reports about fatigue fracture properties. According to our previous study, they presented a problem of low fatigue strength compared to wrought material. In this study, to improve the fatigue strength of Ti-6Al-4V compacts by MIM process, a little amount of boron was added by using TiB2 powder. Boron showed the effect of refining the grain size of lamellar structure of Ti-6Al-4V compacts, which lead to increase the fatigue strength.