The invention relates to a method for producing 2-keto-L-gulonic acid-C.sub.4 C.sub.10 alkyl ester by esterifying 2-keto-L-gulonic acid (KGS) with an unsaturated, branched or unbranched C.sub.4 C.sub.10 alcohol. The inventive method is characterized by the fact that an aqueous KGS solution is reacted with a C.sub.4 C.sub.10 alcohol up to an esterification degree of 20 to 70 percent in a pre-esterification process carried out under acidic catalysis conditions; and the obtained product is dehydrogenated with an unsaturated, branched or unbranched C.sub.4 C.sub.10 alcohol in a continuous rectification device, whereby the esterification reaction continues, n-butanol preferably being used as the alkyl alcohol. In a preferred embodiment, the aqueous KGS solution is concentrated up to or beyond the limit of solubility prior to the esterification process, preferably by catalyzing a homogeneous or heterogeneous catalyst, especially sulfonic acid, at temperatures of 50 to 120.degree. C. In another embodiment, the produced KGS ester is reacted in one or several additional steps so as to obtain L-ascorbic acid.