Abstract: To improve the low mechanical properties of the welded steel/Al dissimilar joints, effects of different welding speeds on the weld shape, interface microstructures and mechanical properties of the steel/Al lapped joints were studied by using fiber laser keyhole welding process without any filler materials. Results show that the weld appearance of the joints is improved with increasing welding speed from 2.4 m/min to 3.3 m/min. A smooth weld can be achieved under the condition of welding speed of 3.0 m/min and 3.3 m/min. Intermetallic compound layers composed of Fe₂Al₅ and Fe₄Al₁₃ phases are formed at the interface of the steel/Al joints. The quantity of Fe₄Al₁₃ phases and the thickness of the Fe₂Al₅ layers at the interface decrease with the increase of the welding speeds. The tensile shear tests show that the highest mechanical resistance of 137.1 N/mm can be obtained for the steel/Al joints at a welding speed of 3.0 m/min.