Recent work at this laboratory on downstream acoustic excitation of a confined 2-D laminar premixed flame showed tilting and shrinking/elongation of the flame on a time-averaged basis.1 Shadowgraph images of the flame revealed that the jet of hot combustion products from the flame may be responding to the acoustic field by tilt and spreading at different rates depending on the acoustic frequency. The present study, therefore, examines the effect of downstream acoustic excitation on the near-exit plane flow structures of a laminar 2-D jet confined in a rectangular duct. The focus here is on low aspect ratio and low Reynolds number jet. Acoustic excitation from 400 to 800 Hz in steps of 50 Hz is employed. The effect of forced oscillation on an air or He jet in the presence and absence of air co-flow are studied. FJow field visualization of the jet mixing is performed using acetone-PLIF technique. The phenomena of jet tilt and spread are observed in the current study. Image processing of the PLIF images is employed to quantify these phenomena under the present test conditions. The vortex shedding distance from the burner lips and the length of the potential core is observed to decrease in the presence of the acoustic field. The results obtained are compared with the effect of forcing on a premixed flame at very similar conditions. It is seen that jet tilting phenomenon is observed at the same excitation frequencies as observed for flame tilting. It is also seen that the excitation frequencies which reduced the flame height also exhibit the phenomenon of greater jet spread due to acoustic forcing.