A concise, easily scalable synthesis of a rare ketohexose, D-tagatose, was developed, that is compatible with the preparation of D-[UL-13C6]tagatose. Epimerization of the widely available and inexpensive ketohexose D-fructose at the C-4 position via an oxidation/reduction (Dess-Martin periodinane/NaBH4) was a key step in the synthesis. Overall, fully protected natural D-tagatose (3.21 g) was prepared from D-fructose (9 g) on a 50 mmol scale in 23% overall yield, after five steps and two chromatographic purifications. D-[UL-13C6]Tagatose (92 mg) was prepared from D-[UL-13C6]fructose (465 mg, 2.5 mmol) in 16% overall yield after six steps and four chromatographic purifications.