Abstract: Biocatalysts are important for the industrial processes of biocatalysis. The production processes are carried out at a high concentration of substrate or product，high ion concentration，in an acidic or alkaline solution，even in an organic medium for some special substrates，and are of considerable economic significance because of high conversion efficiency. The discovery and development of effective biocatalysts are the key point of practical processes of biocatalysis. Extremophiles have been considered as an important source of effective biocatalysts. This review focuses on the discovery and development of some useful biocatalysts from thermophiles，halophiles，radioresistance extremephiles，organic-solvent tolerant microorganisms. The main emphasis is put on some comprehensive examples concerning some unique biocatalysts and their effective bio-conversion. The future prospects of extremophiles as abundant resources for the industrial effective biocatalysts are addressed.