Site-directed mutagenesis has become the conventional means to study the structure and function ofenzymes. It has been widely used to change the characteristics of enzyme. In vitro molecular directed evolution of enzymeis a new strategy in the engineering of novel biocatalysts, which mainly mimics the process of natural evolution to generaterandom mutation in the genes coding for useful enzymes by the techniques of error-prone PCR, and then in vitro recombinespositive mutations through various methods such as DNA shuffling, staggered extension process, random-primingrecombination, and incremental truncation. Finally, the desired enzymes may be obtained by selection and screening. Recentadvances and applications in the directed evolution of enzyme are reviewed.