Metal/metal oxide nanomaterials have gained significant attention across various fields physical and chemical properties. The biosynthesis of metal/metal oxide nanoparticles by microalgae aligns with the principles of green chemistry, showcasing remarkable potential for diverse applications. The mechanisms involved in microalgae-mediated synthesis of metal/metal oxide nanoparticles was summarized, which could be classified into intracellular and extracellular pathways. In the intracellular process, active microalgal cells utilize electrons generated through the photosynthetic electron transport chain to reduce captured metal ions, or they produce bioactive substances such as phytochelatins and metallothioneins that bind to metal ions, forming low-toxicity composite nanoparticles. On the other hand, extracellular synthesis employed bioactive compounds such as proteins, flavonoids, polyphenols, and tannins from microalgal extracts to reduce and cap metal ions, resulting in stable nanoparticles. The influence of various factors was discusses, including microalgal species, culture conditions (light intensity, temperature), and synthesis parameters (pH, reaction time, and temperature), on nanoparticle size, morphology, and properties. Additionally, it highlighted recent advances in the application of microalgaebased nanomaterials in antibacterial technology, environmental remediation, and biomedicine. Finally, based on the current trends and technical challenges in the development of microalgae-based nanomaterials, future research directions were proposed, providing theoretical and practical guidance for further advancements in this field.