In this study, B powders of different contents are added into TC4 powders and the laser additive manufacturing (LAM) experiment is conducted. Influence of the addition of B on the microstructure and mechanical properties of samples is investigated. Results show that the addition of trace B can effectively refine the microstructure size of TC4 alloy produced using LAM. The growth of the prior-β grains in LAM-TC4 alloy is restrained by an addition of 0.05% B, and the grain width is significantly decreased. An addition of 0.1% B can promote the transformation from coarse prior-β crystals to equiaxed crystals and result in a great reduction of the size of α bundle. Plasticity of the TC4-0.05B alloy is evidently improved compared with that of the boron-free TC4 alloy, whereas the change in the strength is not significant. Anisotropy of the as-deposited TC4-0.05B alloy and TC4-0.05B-solution aging is low.