A rare aldotetrose, L-erythrose, was produced from erythritol via a two-step reaction. In the first step, complete oxidation of erythritol to L-erythrulose was achieved by using Gluconobacter frateurii IFO 3254. Washed cell suspension of the strain grown on tryptic soy broth (TSB) supplemented with 1% D-sorbitol was used to carry out the transformation reaction at 30 degreesC with shaking at 170 rpm. At 10% substrate concentration, 98% erythritol was converted to L-erythrulose within 48 h. The produced L-erythrulose was then used as a substrate for the production of L-erythrose. The isomerization of L-erythrulose to L-erythrose was carried out using constitutively produced L-ribose isomerase (L-RI) from the mutant strain Acinetobacter sp. DL-28 grown on D-lyxose mineral salt medium. At equilibrium, the yield of L-erythrose from L-erythrulose was 18% and finally 1.7 g L-erythrose was obtained from 10 g erythritol. After a number of simple purification steps, the product was isolated from the reaction mixture by ion-exchange column chromatography (Dowex 50W-X2, Ca2+). The structure of the product was determined after NaBH4 reduction from Infrared (IR) and C-13 nuclear magnetic resonance (NMR) spectra.