This paper has dealt with the feasibility of friction-stir welding a zinc-coated steel plate to a pure aluminum plate in a lap joint configuration (the aluminum plate was top and the steel bottom). The friction stir welding was carried out at rotation speeds of 16.7-41.7 s-1 and travel speeds of 3.3-5 mm/s. It was found that the performance of the joint depended strongly on the depth of the pin tip of the FSW tool relative to the steel surface; when the pin depth did not reach the steel surface the joint showed quite weak fracture loads, while the penetration of the pin tip to a depth of 0.1 mm under the steel surface significantly increased the joint strength. The joint strength tended to increase with rotation speed and slightly decrease with the increase in the traveling speed. As compared with the similar joints of an aluminum to a steel without Zn-coating, joints of aluminum to the Zn-coated steel exhibited high strength at all bonding parameters employed in this investigation, which suggested the beneficial effect of the Zn coating on the bond strength.