For an unbaffled agitated vessel with an angularly oscillating impeller whose rotation continues while periodically reversing its direction at a set angle, the progress of mixing of Newtonian liquid phase was studied experimentally in relation to the impeller power characteristics. Results obtained for the angular oscillation mode of a disk turbine impeller with six flat blades with different amplitudes (Strouhal number) were compared to those obtained for the unidirectional rotation mode of the impeller of identical design. Using an angularly oscillating impeller, turbulent and laminar mixings were effective, respectively, with larger and smaller amplitudes. The mixing characteristics for turbulent and laminar flow regions were discussed on the basis of the flow field features, which the impeller power number reflected.