Under mild reaction conditions (170 degrees C, 3 MPa), glycerol is hydrogenolyzed to 1,2-propanediol with very high selectivity at high conversion using Ru/TiO2 as catalyst in basic aqueous solution. The base aids the initial dehydrogenation of glycerol to glyceraldehyde and promotes the dehydration of glyceraldehyde to 2-hydroxyacrolein.