The work explores the three-dimensional structure of the near field of a quasi-two-dimensional turbulent jet. The jet stream forms at an outflow from the rectangular channel with aspect ratio B/h equal to 1:2.5 into the channel, formed by two plane-parallel plates. The experiments were carried out for a wide range of Re number from 2 000 to 20 000. The measurements were performed using Tomographic PIV method with high time resolution. It is shown that for the whole investigated range of Re number in the near-field of the quasi-two-dimensional jet, there are formed secondary flows, caused by the presence of longitudinal vortex structures in the flow.