Crystals of methyl 4,6-dichloro-4,6-dideoxy-α-D-glucopyranoside are monoclinic, a= 16·51, b= 5·06, c= 13·16 Å, β= 115·6°, Z= 4, space-group C2. The structure was determined with Mo-K_α scintillation counter data by Patterson and Fourier methods, and refined by least-squares, the final R being 0·09 for 544 observed reflexions. The absolute configuration was determined by the anomalous dispersion method (Cu-K_α radiation). The molecule has the normal chair conformation, and the bond distances and valency angles are similar to those in related compounds.