Formability of AZ91D alloy by casting - forging process was investigated. The ingots for forging were fabricated by gravity casting. The dimensions of the ingots were 30 mm and 40 mm. in diameter and 150 mm in length.. The grain sizes of the castings were about 250 mum (phi40 ingot) and 200 mum (phi30 ingot), respectively. They were cut off and forged into cup-shaped products at temperatures of 673 K and 573 K and at ram speeds of 1 and 50 mm/min. The billet of the phi40 ingot was forged directly to the cup and some cracks occurred at the top end in some forging conditions. On the other hand, the billet of the phi30 ingot was forged after pressing to 40 mm, no cracks occurred in all conditions. The grain size of the specimen forged from the phi30 billet at the temperature of 673 K and ram speed of I mm/min was 25 mum; it was 43 mum in the specimen forged from the phi40 billet at similar conditions. Because of the grain refinement during pressing prior forging, the products from the phi30 billet exhibited better formability than that from the phi40 billet.