Abstract: In higher plant, Δ9 desaturase introduces the first double bond into saturated fatty acids, resulting inthe corresponding monounsaturated fatty acids.We have cloned gene, designated as PvfadA, for C18∶0Δ9 desaturase catalytic activity from Pavlova viridis by RT-PCR, RNA ligase mediated RACE (RLM-RACE) and Overlap-PCR strategy. This desaturase, when expressed in Escherichia coli, desaturated stearic acid to yield oleic acid, but did not desaturate other fatty acids in E. coli. These results indicate that PvFadA is specific to stearic acid. The deduced amino acid sequences of PvFadA show that a putative (D /E) X2HX～100(D /E) X2 H metal binding motif, which specifically existed in acyl-ACP desaturase. Moreover, Amino acids of PvFadA are similar in part to those of acyl-ACP desaturases from higher plant, such as A rabidopsis thaliana, Oryza sativa and Glycine max, but not to those of acyl-lipid desaturases of Cyanobacteria, and acyl-CoA desaturases of higher plant. In addition, the 3D2model structure of PvFadA is composed of 11 helixes, moreover, α3, α4, α6 andα7 form a core 42helix bundle to regards as an active center in this enzyme, similar as acyl-ACP desaturase of Ricinus communis and M ycobacterium tuberculosis H37Rv.