An acyl-CoA-Delta 9 desaturase from Saccharomyces cerevisiae was expressed by subcellular-targeting in soybean (Glycine max) seeds with the goal of increasing palmitoleic acid (16:1 Delta 9), a high-valued fatty acid (FA), and simultaneously decreasing saturated FA in oil. The expression resulted in the conversion of palmitic acid (16:0) to 16:1 Delta 9 in soybean seeds. 16:1 Delta 9 and its elongation product cis-vaccenic acid (18:1 Delta 11) were increased to 17 % of the total fatty acids by plastid-targeted expression of the enzyme. Other lipid changes include the decrease of polyunsaturated FA and saturated FA, suggesting that a mechanism exists downstream in oil biosynthesis to compensate the FA alternation. This is the first time a cytosolic acyl-CoA-a dagger 9 desaturase is functionally expressed in plastid and stronger activity was achieved than its cytosolic expression. The present study provides a new strategy for converting 16:0 to 16:1 Delta 9 by engineering acyl-CoA-Delta 9 desaturase in commercialized oilseeds.