The microstructure, mechanical property and corrosion behavior of AZ91D with addition of lanthanum were investigated. With adding 1% lanthanum, the ultimate tensile strength and the elongation increased by 21.1% and by 101.2%, respectively. This mainly caused by the refinement of the beta phase and the formation of Al11La3 strengthening phase. With adding 1% lanthanum in AZ91D alloy, the weight loss corrosion rate decreased to 47.2%. But when lanthanum content is over 1%, the corrosion rate increased. Small amount of lanthanum could form the small beta phase similar to reticular structure, which could restrain the corrosion at some extent; large amount of lanthanum caused the depletion of aluminum in alpha matrix, which increased the corrosion rate.