The invention relates to a casting nozzle for a horizontal strip casting system, in particular for casting steel strip, wherein the nozzle is designed as a narrow rectangular hollow block having a bottom, top and two side walls and made of refractory material, the outflow region being located only slightly above a cooled continuous belt receiving the outflowing melt. Viewed in the flow direction, it is provided that the clear cross-section of the hollow block in the outflow region reduces uniformly in the direction toward the outflow and the end face of the bottom of the hollow block is designed with respect to the surface of the continuous belt such that the melt contacts the continuous belt perpendicularly.