In this study, depth sensing nano-indentation test was carried out to investigate the plastic/viscoplastic behavior of beta titanium alloy. The indentation experiment results showed that both hardening and softening effect existed in indentation process and the residual penetration depth was deeper when the nominal indentation strain rate increased. That is opposite to the room temperature tension test results, which showed a strain rate hardening behavior. FEM simulation combined with viscoplastic model was carried out to simulate the indentation procedure. FEM results showed that the pile-up pattern changed with the consideration of the nominal indentation strain rate effect. Atom force microscope (AFM) observation gave a same result of pile-up patterns.