This research has been investigated fluidity and microstructures characteristics of AZ 91 D alloy using new type semi-solid injection machine. To ensure good casting products, uniform temperature distribution was required during heating in the injection cylinder of this machine. So, the injection cylinder was divided with six heating zones. Then temperature distribution in the injection cylinder was precisely controlled. AZ 91 D billets were heated to the desired temperatures in the injection cylinder, and injected into the permanent mold with injection speed about 430 mm/s. Fluidity was measured by using spiral permanent mold with the cavity of 1045 mm in length and 5 mm in thickness. The fluidity test has been done with the fraction solid from 0% - 60%. The fluidity was 905 to 153 mm for fraction solid 0% to 60%, respectively. At the fraction solid from 50% to 60% microstructures are consisted of spherical solid particles and the solid particles surrounded by liquid phase. The shape of solid particles begins to change at the fraction solid of 40%.