It is an object to provide an L-ascorbic acid derivative which can keep the L-ascorbic acid stable to heat and light and thus has a long shelf life, which is high in permeability into the skin, which can be quickly hydrolyzed by phosphatase, an enzyme that is ubiquitous in vivo, and which exhibits physiological activities that are inherent to L-ascorbic acid and beneficial to health, a method for producing such an L-ascorbic acid derivative, and a skin-whitening cosmetic material.There is provided an ascorbic acid derivative comprising an L-ascorbic acid-2-phosphate ester or a salt thereof wherein the phosphate ester has a branched alkyl group, the L-ascorbic acid-2-phosphate ester being of formula [13]. The ascorbic acid derivative is produced by a method comprising reacting a branched alkanol with phosphorus oxychloride to synthesize monoalkyldichlorophosphate or dialkylmonochlorophosphate, reacting the thus obtained substance with 5,6-O-isopropylidene-L-ascorbic acid obtained by reacting L-ascorbic acid with acetone, and subjecting the thus obtained substance to acid hydrolysis. There is also provided a cosmetic material containing such an ascorbic acid derivative by 0.05 to 80 percent by weight. ##STR00001## (wherein each of R.sup.1 and R.sup.2 is a hydrogen (H) atom or an alkyl group having branches and including 3 to 30 carbon atoms, but not both of R.sup.1 and R.sup.2 are hydrogen (H) atoms).