The dissimilar joining of aluminum (AA 1100) to brass (UNS C27000) in the electric power industry is highly required to transmit the electricity efficiently. However, it's hard to join these materials using fusion welding process because of the broad differences in their physical, mechanical and chemical properties, and the evaporation of zinc constituent during the welding process. Thus, it is directed the researchers to find a new technique to tackle this problem. It seems that ultrasonic metal welding (USMW) is one such promising method that is developed nowadays. In this study, lap joints of AA 1100 aluminum alloy and UNS C27000 copper alloy have been produced using USMW and the effects of process parameters on the mechanical strength and interface microstructure have also investigated. The tensile shear failure load firstly increases with the rise of weld time up to 0.55 s of weld time followed by a rapid decrement in the value due to excessive plastic deformation in the weld zone. It is confirmed from the energy dispersive X-ray spectroscopy (EDX) and X-ray diffraction analysis (XRD) results that USWed aluminum to brass produces intermetallic compounds (IMC), and its thickness is getting wider with the increase in weld time. A composite eutectic structure of Al and Al2Cu is the first compound formed in the middle of the weld zone.