Ti-6Al-4V titanium alloy manufactured by selective laser melting (SLM) has a unique structure and properties. They offer a higher yield and ultimate tensile strengths but lower ductility than traditionally processed samples. SLMed Ti-6Al-4V alloys induced increased ductility but decreased tensile strengths after thermal treatment at 840 °C for 2 hours. Sliding wearing tests and cutting experiments were conducted to further understand the effects of heat treatment on machinability. The result showed that as-built SLMed Ti-6Al-4V samples presented lower coefficients of friction but higher wear rates than heat-treated ones due to their delamination caused by cracks. Cutting forces of as-built samples were lower during milling than that of heat-treated samples. Nevertheless, better surface roughness was produced when heat-treated samples were machined. Moreover, the optimal cutting parameters for both materials were the same.