Delta 6-fatty acid desaturase (D6DES) is used in the synthesis of polyunsaturated fatty acids (PUFAs) from microorganisms to higher animals, including arachidonic acid (ARA) and eicosapentaenoic acid (EPA). A 1,338 bp full-length cDNA encoding D6DES was cloned from Acanthopagrus schlegeli (AsD6DES) through degenerate- and RACE-PCR methods. A recombinant vector expressing AsD6DES (pYES-AsD6DES) was subsequently constructed and transformed into Saccharomyces cerevisiae to test the enzymatic activity of AsD6DES towards the production of n-6 and n-3 fatty acids. The exogenously expressed AsD6DES produced gamma-linolenic acid (18: 3 n-6) and stearidonic acid (18:4n-3) at 26 and 36% from exogenous linoleic acid (18:2n-6) and alpha-linolenic acid (18:3n-3), respectively, indicating that it is essentially a delta 6-fatty acid desaturase.