阿拉伯糖，又称树胶醛糖、果胶糖，是一种戊醛糖：含有5个碳原子并且带有醛基的单糖。分子式C₅H₁₀O₅，分子量150.131。

阿拉伯糖有8种立体异构体，常见的为β-L-阿拉伯糖（CAS号：87-72-9，比旋光度：+190.5°→+104.5°）和β-D-阿拉伯糖（CAS号：10323-20-3，比旋光度：-175°→-108°）。天然的L-阿拉伯糖广泛存在于食物中，通常与其他单糖结合，以杂多糖的形式存在于胶质、半纤维素、果胶酸、细菌多糖及某些糖苷中。D-阿拉伯糖通常由人工合成而得，在自然界很少见，偶见于某些大肠杆菌或结核杆菌的细胞内。

Arabinose is an aldopentose – a monosaccharide containing five carbon atoms, and including an aldehyde (CHO) functional group.

For biosynthetic reasons, most saccharides are almost always more abundant in nature as the "D"-form, or structurally analogous to D-glyceraldehyde. However, L-arabinose is in fact more common than D-arabinose in nature and is found in nature as a component of biopolymers such as hemicellulose and pectin.