Octadecylphospho-L-serine (OPS), belonging to the family of alkylphosphate esters with anticancer activity, was synthesized by transesterification of octadecylphosphocholine using phospholipase D (PLD). With respect to the yield of product, PLD from cabbage proved to be superior to PLD from Streptomyces spp. Although the addition of n-hexane/2-octanol is advantageous to suppress the hydrolytic byproduct, a purely aqueous reaction medium was preferred because of better recovery of the product.