Ribose is the monosaccharide (sugar) appearing in RNA (hence the name "ribose nucleic acid"). Its chemical formula is $\mathrm{C}_{5}\mathrm{H}_{10}\mathrm{O}_{5}$.

Like deoxyribose, ribose is centered in a five-carbon ring, whose carbon atoms are numbered clockwise 1', 2', 3', 4', and 5'. Also like deoxyribose, ribose is chiral, meaning that its mirror image exists as well. Thus, "ribose" actually refers to two different molecules, D-ribose and L-ribose. D-ribose is the molecule appearing in RNA, whereas its mirror image L-ribose does not occur naturally and has not been applied synthetically.

However, ribose differs from deoxyribose in that its 2' carbon is bonded to a hydroxyl group (OH) instead of to a hydrogen atom (H).