Recent advances in microreactor technologies have enabled innovative approaches for synthesizing nanoparticles. These techniques provide precise control over reaction parameters, product quality, safety, and overall reaction efficiency. This chapter introduces the recent developments in nanoparticles synthesis using microreactors, including gas–liquid segmented, continuous-flow, and droplet-based systems. Microreactor-based production methods of various types of nanoparticles, including metallic, semiconductor, magnetic, organic, and hybrid, with varying sizes, shapes, crystalline structures, and surface chemistries are also discussed. Additionally, this chapter introduces the challenges and limitations of microreactor-based nanoparticles synthesis methods.