The intermetallic compound (IMC) layer, tensile properties, and fracture behavior of dissimilar Mg/Al joints and their relationship during linear friction welding (LFW) are investigated to develop a strategy to obtain high-strength Mg/Al dissimilar materials. The thickness of the Mg/Al-based IMC layer decreases as the applied pressure increases and the frequency decreases. The IMC layer is mainly composed of Mg17Al12 and Mg2Al3 at the weld interface. The tensile strength of the joints fabricated at an appropriate frequency of 50 Hz and a high pressure of 200 MPa during LFW is 235 MPa, which is 94 % the tensile strength of AZ31 and is attributed to the effective suppression of the Mg2Al3 IMC layer growth. At a lower frequency, large defects and pores are formed near the weld interface edge on the Mg side owing to the low welding temperature. The joint fabricated at a higher frequency exhibits a thick and brittle Mg2Al3 IMC layer at the weld interface because of the high growth rate; thus, the dissimilar joints fractured primarily at the Mg2Al3 IMC layer. The inhibition of the Mg2Al3 IMC layer growth yields superior tensile properties in Mg/Al dissimilar materials.