The bolt load loss behavior of AZ91D magnesium alloy bolted joints with a conventional SCM435 steel bolt and an A5056 aluminum bolt was investigated at elevated temperature. The A5056 bolt could reduce the bolt load loss compared to the SCM435 bolt due to smaller mismatch of thermal expansion between the bolt material and the plates. The mismatch of thermal expansion between bolt material and AZ91D plates was found to induce the compressive creep deformation in the AZ91D plates which performed as the main mechanism of bolt load loss. At higher tightening stress, the bolt load loss could be intensified by additional plastic deformation in bolt occurred during the test. Moreover, it is suggested that the plastic deformation could be reduced by decreasing the friction condition in the bolted joint.