AZ91 magnesium alloy was prepared by spray forming. The spray-deposited alloy was subsequently hot-rolled with a 80% reduction at 350 ℃. The microstructural features of the as-spray-deposited and hot-rolled alloy were examined by optical microscopy, scanning electron microscopy and X-ray diffractometry. The results show that the spray-formed AZ91 magnesium alloy has, compared with the as-cast ingot, a finer microstructure with less intermetallic phase Mg17Al12 dispersed in the matrix due to fast cooling and solidification rates of spray forming process, and, therefore showing excellent workability. It can be hot-rolled with nearly 20% reduction for one pass at lower temperatures (330-360℃), and the total reduction can reach 50% prior to annealing. After proper thermo-mechanical treatment, the spray-formed AZ91 magnesium alloy exhibits outstanding mechanical properties.