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This paper presents the velocity and vorticity fields of a supersonic, pulsed co-flow injection system, measured using particle image velocimetry (PIV). The active injection system consists of an actuation air jet from a nozzle (1 mm ID, 1.5 mm OD) that provides large mean and fluctuating velocity profiles to the shear layers of a fluid stream injected through a 460 μm diameter annular space surrounding the nozzle. The injector assembly is designed to operate in three modes in the present study. In the first case, annular fluid was injected at 70 m/s without actuation and treated as baseline flow. In the second case, a steady under-expanded supersonic jet with an exit velocity of 350 m/s interacts with the injected annular fluid. In the last case, the actuation jet pulsing at 15.5 kHz introduces highfrequency streamwise vortices and shockwaves to the annular stream. PIV data indicate that steady and pulsed actuation significantly modifies the velocity and vorticity fields of annular flow. While steady actuation caused intensive shear and high vorticity streaks in the flow, the high-frequency vortex generated in pulsed actuation resulted in highly fluctuating velocity and vorticity fields that favor enhanced mixing between the annular stream and supersonic actuation jet. Quantitative data from this study confirm the potential of this injector system for flow mixing and control under extreme conditions.