Nuclease is obtained from the freeze-dried extract of Penicillium citrinum medium. It can hydrolyze nucleic acid to 5`-nucleotide orientately. As we all know, the 5`-nucleotide which is a valuable flavor enhancer of food can effectively enhance flavor. Nuclease can be applied for improving flavor and inhibiting off-flavor. Meanwhile, the nucleic acid can enhance the sweet and meat tastes. So Nuclease has an important role in the industrial Production of 5`-nucleotide and the seasonings such as yeast extract.