Additive manufacturing (AM) of metallic materials is attractive processing for biomedical implants and aviation components. However, fatigue life of AM parts are remarkably weak. Mechanical surface treatment such as cavitation peening, shot peening and laser peening can improve the fatigue life of AM parts. In the present paper, in order to demonstrate the fatigue life enhancement of AM parts by various peening methods, titanium alloy Ti6Al4V manufactured by electron beam melting EBM was treated by cavitation peening, shot peening and laser peening, and then tested by a plane bending fatigue test. And also, in order to make clear mechanism on the fatigue life enhancement of AM parts, mechanical properties such as residual stress, yield stress and hardness were evaluated, and the correlation between the mechanical properties and the fatigue life was investigated. Note that the yield stress was evaluated by an inverse analysis using an indentation test. It was concluded that the fatigue life of Ti6Al4V manufactured by EBM was proportional to a parameter defined by residual stress, yield stress, surface roughness and hardness.