In this study, the inhibiting effect of cerium ions (Ce(3+)) on corrosion of 3003 aluminum alloy (AA3003) in ethylene glycol-water solutions was investigated using a rotating cylinder electrode, simulating the hydrodynamic condition of the automotive cooling system. Electrochemical measurements and surface characterization were conducted to study the inhibiting mechanism of Ce(3+) on the Al alloy corrosion. It is found that Ce(3+) serves as a cathodic inhibitor, and inhibits effectively corrosion of AA3003 in the flowing ethylene glycol-water solutions. The inhibiting effect of Ce(3+) is resulted from the formation and deposit of Ce oxide and/or Ce hydroxide on the electrode surface. With the immersion time, the Ce deposit layer increases its thickness to cover the second phase particles, eliminating the galvanic coupling effect between the second phase particles and Al alloy substrate.