Ti addition to AZ91 alloy was been investigated with conventional casting. The Corrosion resistance of all the different Ti addition content alloy was studied in 3.5% NaCl solution through weight loss measurement in constant immersion conditions and potentiodynamic polarization experiments.The results show that addition of Ti with an amount of 0.1~0.8wt% the corrosion resistant of alloy was improved. In the case of AZ91-0.8Ti alloy had minimum corrosion rate value , AZ91-0.4Ti alloy had minimim corrosion current density. After Ti added into alloy, the morphology of β phases was changed, TiAl3 intermetallics appeared. The inhibiting effect of the β phases and TiAl3 intermetallics in the AZ91-Ti alloy predominated in the long period immersion testing, but during short interval of electrochemical testing galvanic corrosion effect in the AZ91-Ti alloy predominated.