This paper presents the effect of longitudinal acoustic fields on jets. In these experiments a jet is established in a transparent test section in which an acoustic field is setup using acoustic drivers. Flow visualization and PIV measurements indicate that the acoustic oscillations decrease the core length and increase the jet spread, indicating that the mixing was enhanced by the acoustic field. The enhancement of mixing was greatest for Strouhal numbers between 0.2 and 0.3. At these Strouhal numbers, flow visualization indicates the presence of side jets. Velocity data shows that strong velocity oscillations results in accumulation of jet fluid ahead of the ring structure leading to the generation of the side jet. It is shown that the strong entrainment of the surrounding fluid by the ring vortex followed by the formation of side-jet evolution and the high velocity gradients introduced by the acoustic field results in intense mixing. It is observed that at very high acoustic amplitudes the ring vortex gets distorted and breaks up from the jet leading to further increase in mixing. © 2003 by R. I. Sujith. Published by the American Institute of Aeronautics and Astronautics, Inc.