l‐[4‐13C]Glutamine was synthesized from sodium [2‐13C]acetate in 12 steps and 18% overall yield. A Wittig reaction of (R)‐benzyl 4‐formyl‐2,2‐dimethyloxazolidine‐3‐carboxylate and ethyl 2‐(triphenylphosphoranylidene)[2‐13C]acetate prepared from d‐serine and sodium [2‐13C]acetate, respectively, gave (4S)‐4‐(2‐ethoxycarbonyl[2‐13C]vinyl)‐2,2‐dimethyloxazolidine‐3‐carboxylic acid α,β‐isopropylidene group, oxidation of the resulting hydroxyl group to a carboxyl group and transamidation of the ester moiety gave l‐N‐Cbz‐[4‐13C]glutamine (Cbz = benzyloxycarbonyl). Finally, removal of the Cbz group gave l‐[4‐13C]glutamine. l‐[4‐13C]Glutamine can be prepared in fewer steps and higher yield by this method compared with previously reported methods.