Extreme enzymes have super biological stability. They demonstrate biological activity at extreme temperatures, pH, pressure and ionic intensities. Thus, extreme enzymes provide good opportunities for biological catalysis and transformation. The discovery of the new extreme species, the confirmation of the genome sequence and the application of gene engineering technology have expedited the discovery and preparation of the new enzymes. Protein engineering and directed evolution further alter the enzymatic activity and peculiarity of the extreme enzymes, which fosters the industrial application of the extreme enzymes. Research on extreme enzymes increases comprehension of the mechanism of enzymatic stability and enriches the theory of molecular evolution.