An ultrafine grained Mg-9Al-1Zn magnesium alloy with the mean grain size less than 1 μm was produced by using high-ratio differential speed rolling. The processed alloy exhibited excellent superplasticity at relatively low temperatures. The micro-forming tests were carried out using a micro-forging apparatus with micro V-grooved shaped dies made of silicon and the micro-formability was evaluated by means of micro-formability index, Rf (=Af/Ag, Af: formed and inflowed area into the V-groove, Ag: area of the V-groove). The Rf value increased with temperature up to 280℃ and then decreased beyond 300℃. The decrease of the Rf value at 300℃ was attributed to the accelerated grain coarsening. Increasing the micro-forging pressure increased the Rf values. At a given die geometry, die filling ability decreased as the die position moved away from the die center to the end. FEM simulation predicted this behavior and a method of improving this problem was proposed.