Abstract: This paper investigates the interfacial microstructure and mechanical properties of Al/Mo dissimilar joints produced by brazing with Al-Si filler metals. Two brazing processes were employed, namely direct brazing and brazing with a pre-deposited Ni coating on the Mo substrate, using Al-12Si as the filler metal to join aluminum and molybdenum. Emphasis is placed on the influence mechanisms of holding time (15 min and 30 min) and interfacial structure (with or without Ni interlayer) on the interfacial microstructure, elemental diffusion behavior, and mechanical properties of the joints. The results show that during the joining process, Al-12Si filler metal forms intermetallic compounds such as Al₁₂Mo, which promotes metallurgical bonding at the interface. The addition of Ni further improves the distribution of Si and enhance the diffusion ability of elements from the aluminum side to the molybdenum side. Microhardness and nanoindentation tests show that the hardness of the intermediate transition layer is moderate, effectively alleviating the hardness difference between aluminum and molybdenum. XRD analysis confirms that stable intermetallic compounds are formed at the joint interface. Combined with thermodynamic calculations, the enthalpy of formation of Al₁₂Mo is negative, indicating its high thermodynamic stability, which is consistent with the XRD results. This research provides experimental basis and theoretical reference for the reliable joining of Al/Mo heterogeneous materials.