Abstract: Investigations on butt fusion welding characteristics of AZ31B magnesium alloy to steel with Ni interlayer were carried out by utilizing the gradient energy density characteristic of laser-TIG heat source. The tensile strength and microstructure of the joint were examined by electronic tension machine, scanning electron microscopy (SEM) and X-ray diffraction (XRD). Results indicated that magnesium alloy can be butt joined to steel by hybrid laser-TIG welding with good Mg/Fe interface by using Ni foil as the interlayer. At the same time, tests showed that a distinct transition zone consisting of Fe, Ni and Al elements forms at the steel side nearby the interface; the microstructure of the joint is mainly composed of α-Mg and a large number of small white particles which are mainly composed of AlNi phase and dispersively distributed. The joint fractures nearby the Mg/Fe interface and the fracture surface shows a typical quasi-cleavage crack. The average of the joint tensile strength is 232 MPa, which is about 90% of the magnesium base metal.