A Mg(65)Cu(25)Gd(10) alloy is produced under the form of 6 mm diameter amorphous rod and its ability to be formed at high temperature is studied. In the supercooled liquid region, the usual transition between Newtonian and non-Newtonian behaviors is detected as a function of temperature and strain rate. A particular attention is also given to the effect of partial crystallization on the high temperature deformation of the alloy: large viscoplastic deformation ability is maintained up to relatively high crystal fraction. The main effect of crystallization on mechanical behavior is a reinforcement effect, which can vary with experimental conditions. Finally, crystal volume fractions are roughly estimated by a simple model used to predict reinforcement due to the dispersion of particles in a viscous matrix.