AZ91 alloys were prepared by hot extrusion and its microstructure and tensile behavior at room temperature were investigated. Compared to as-cast ingot, the grain size of hot-extruded material is more refined, the intermetallic phase Mg17Al12 is broken and dispersed discontinuously. Both strength and elongation of AZ91 are improved by hot extrusion. Tensile behavior and fracture surface of the experimental material were studied. Due to the change in microstructure, the fracture mechanism of extruded material is different from that of as-cast ingot, the latter is mainly a brittle fracture. Ductile fracture plays a role in hot-extruded AZ91 failure at room temperature. AZ91 alloys were prepared by hot extrusion and its microstructure and tensile behavior at room temperature were investigated. Compared to as-cast ingot, the grain size of hot-extruded material is more refined, the intermetallic phase Mg17Al12 is broken and dispersed discontinuously. Both strength and elongation of AZ91 are improved by hot extrusion. Tensile behavior and fracture surface of the experimental material were studied. Due to the change in microstructure, the fracture mechanism of extruded material is different from that of as-cast ingot, the latter is mainly a brittle fracture. Ductile fracture plays a role in hot-rolled AZ91 failure at room temperature.