Digital particle imaging velocimetry (DPIV) was used to measure the transient and time-averaged flow field in the mixing region and the wake of a square jet into crossflow at jet-to-crossflow velocity ratio (VR) of 0.5 and 2. The phenomenon of vortex instantaneously shedding from the jet hole was investigated

and the flow turbulence intensity was estimated. The complex vortical structures encountered at VR of 2 were analyzed. Compulsively oppressed by the main flow

the jet attached to the wall at VR of 0.5

and lifted off the wall to develope into the main flow at VR of 2. The twisted vortices in the leeward of jet contributed to the transportation of the crossflow boundary-layer fluid into the near wake

causing intensive turbulence. Strong vortices formed near the jet hole soon broke down and dissipated

yet the weak counter-vortex pair still held in the far wake.