This paper presents a theoretical and experimental investigation of the laminar steady 2D-mixing flow in a junction. The numerical method developed by Gosman et al. has been applied to derive velocities and temperatures profiles in the mixing zone. The effects of the angle between the two branches of the junction and the air-flow rate upon the structure flow are analysed, for both forced and mixed convection cases. The experimental procedure is based upon a flow visualization technique and L.D.V. velocity measurements : a reasonably good agreement between theoretical and experimental results is found.