Ultrafine grained commercially pure Ti with different grain size was prepared by Equal Channel Angular Pressing (ECAP). The mechanical properties of commercially pure Ti were investigated by the nanoindentation technique. The effects of loading strain rate and grain size on the nanoindentation measurement of commercially pure Ti were discussed. Strain hardening capacity and residual stress of commercially pure Ti were analyzed. The results show that the hardness of commercially pure Ti increases with the loading strain rate increasing and grain size decreasing. The hardness-dislocation curves exhibit the Indentation Size Effect (ISE) with the incorporated hardening effect. The indentation morphology shows that commercially pure Ti processed by ECAP has little strain hardening capacity and compressive residual stress compared to coarse-grained sample.