Abstract: Large eddy simulations are performed to investigate rectangular jets in crossflow. In particular, the jet-to-crossflow velocity ratio influence on flow dynamic and mixing properties is analysed. Conversely to free jets, Kelvin-Helmholtz vortices do not lead to ring structures, they develop at the windward side of the jet. Their shedding frequency is also different. The Strouhal numbers for both mixing layer and wake structures increase with decreasing velocity ratio. Moreover, the upright vortices appear in the wake zone for the case of lower velocity ratio. The near field initiation of the counter-rotating vortex pair formation is demonstrated in the lower velocity ratio case and dominates in the far field. In the higher one, the jet impinges the opposite wall which inhibits the complete development of such structures in the far field. An enhancement of the mixing process in the case of lower velocity ratio as demonstrated by the rapid jet centerline decay of the passive scalar (temperature) seeded in the jet. As a final result, for the dynamics, the overall agreement of the numerical results and those of literature suggests that the jet mixing layer instability is strengthened as the velocity ratio is decreased. While, the wake structures topology is also strongly dependent on the velocity ratio. The mixing process is enhanced by the presence of the counter-rotating vortex pair.