Micro-friction stir welding of thin aluminum sheets requires precise control of heat generation and longitudinal force, as insufficient heat input may result in insufficient material plasticization, while excessive heat can lead to local thinning, surface defects, or loss of dimensional stability. In this study, a finite element simulation was developed to investigate the thermomechanical response during micro-FSW of 0.6 mm thick 6061-T4 aluminum alloy sheets. The model was used to evaluate the influence of tool rotational speed and welding speed on the temperature field and longitudinal force during welding. The tool used had a pin with a diameter of 3 mm and a length of 0.4 mm, while the tool shoulder diameter was 10mm. The most favorable parameter combination, 750 rpm and 400 mm/min, was selected based on the adopted thermal criterion, while the associated longitudinal force did not correspond to an extreme value within the investigated range. These results suggest that numerical simulation is a useful approach for reducing experimental time and selecting initial conditions for micro-FSW trials, since even a small change in rotational speed or welding speed can abruptly shift the process from a stable state to one with significant defects.