核糖（英语：Ribose）是一种五碳醛糖，一般常见的型态为D-核糖。是RNA的组成物之一，也是ATP及NADH等生化代谢所需分子的原料。

DNA中的核糖是D-核糖，为呋喃型环状结构，该呋喃环状为β构型。由于糖环中5个键均可转动，导致环中各个原子均有不同程度的相对偏离，核糖环不呈一个平面，其中C1’-O4’-C4’这3个原子通常在同一个平面上，而C2’和C3’原子偏离平面，这种偏离使核糖环具有不同的构象，以C5’作为参照来命名核糖环的各种构象。如果C2’或C3’偏离平面的方向与C5’同向，则称为内式（exdo）构象，与C5’反向则为外式（exo）构象。

Ribose is a carbohydrate with the formula C₅H₁₀O₅; specifically, it is a pentose monosaccharide (simple sugar) with linear form H−(C=O)−(CHOH)₄−H, which has all the hydroxyl groups on the same side in the Fischer projection.

The term may refer to either of two enantiomers. The term usually indicates D-ribose, which occurs widely in nature and is discussed here. Its synthetic mirror image, L-ribose, is not found in nature.