Abstract: Selenium is an essential microelement in living organism. Nanosized selenium (Nano-Se or SeNPs) is expected to be the best form of selenium supplement due to its low toxicity and high efficiency. With mild conditions, uniform nanoparticles, good dispersibility and stable structure, SeNPs have great potential in the development of functional products. In this paper, the characteristics of SeNPs, the advantages of microbial synthesis of SeNPs, the types of microorganisms for the synthesis of SeNPs and the development of functional products of Se-NPs are reviewed. And the future researches of the synthesis of SeNPs by microbial transformation are prospected.