Micro friction stir spot welding (mFSSW) is one of the solid-state welding techniques developed to join thin plates with a thickness of less than or equal to 1000 µm. In this study, the effect of mFSSW process parameters on temperature, weld geometry, and tensile strength are investigated. The materials used were aluminum AA1100 and magnesium AZ31B with a thickness of 0.42 mm and 0.5 mm, respectively. The constant parameters of mFSSW were plunge rate of 4 mm/min and high tool rotational speed of 33,000 rpm. The other parameters were tool geometry (pin and pinless), plunge depth (400 and 600 µm), and dwell time (4 and 6 s). The results of this study show that the highest temperature, around 383 C, was at a plunge depth of 600 µm and a dwell time of 6 seconds using pinless tool. The lowest rotational speed, around 19,300 RPM, was at a plunge depth of 600 µm with a dwell time of 4 seconds using a …