The crystal and molecular structure of [beta]-arabinose has been determined more accurately by means of (Fo[long dash]Fc) synthesis in [alpha]-axis and c-axis projections. The hydrogen atoms have been located and included in the calculations, and corrections have been made for individual and anisotropic thermal vibrations of carbon and oxygen atoms. The mean length of C[long dash]C bonds is 1. 535 A, and the mean length of C[long dash]O bonds, excluding C1[long dash]O1, is 1.434 A. The bond C1-O1 is 1. 382 [plus or minus] 0. 012 A, and deviates significantly from the mean value. The mean value of the angles in the pyranose ring (excluding C1[long dash]O5[long dash]C5) is 109. 5[degree], equal to the tetra-hedral angle. The angle C1[long dash]O5[long dash]C5 = 112. 7 [plus or minus] 0. 6[degree] deviates significantly from the mean value, and so does the angle O5[long dash]C1[long dash]O1 = 113.0 [plus or minus] 0. 7[degree]. All the oxygen atoms and hydroxyl hydrogen atoms are engaged in hydrogen bonds, one of which is found to be as long as 3.035 [plus or minus] 0.008 A. O2 takes part in three hydrogen bonds and has roughly tetrahedral surroundings.