The orientation changes during heating of extruded AZ31 were investigated using synchrotron Xrays by in-situ experiments. The as-extruded sample shows a strong <10.0>-fiber texture which is generally observed after round extrusion. The initial <10.0>-fiber texture, in which the <10.0> direction of the hexagonal crystallites is parallel to extrusion direction, starts to change to <11.0>- fiber component at 300 °C. The orientation change rate shows an exponential relation to the heating temperature and the soaking time. The microstructure observations, prior and post heat treatment, indicate that the texture changes occur mainly during grain growth.