透明质酸（Hyaluronan、hyaluronic acid、又称糖醛酸、玻尿酸、琉璃糖碳基酸），是一种是由双糖（D-葡萄糖醛酸及N-乙酰葡糖胺）基本结构组成的糖胺聚糖。透明质酸广泛存在于结缔组织、上皮组织和神经组织中。与多数糖胺聚糖不同，透明质酸不含硫，并在细胞膜而非高基氏体中形成。其相对分子质量可达10量级。透明质酸是细胞外基质的主要成分之一，对细胞增殖和迁移有重要作用，并可能与一些恶性肿瘤的演进有关。

体重75公斤的正常人体内约含16克透明质酸，其中约三分之一每天被分解并重新合成。同时，透明质酸是A群链球菌荚膜的组成成分之一，并被认为和病原体的毒性有关。

Hyaluronic acid (HA; conjugate base hyaluronate), also called hyaluronan, is an anionic, nonsulfated glycosaminoglycan distributed widely throughout connective, epithelial, and neural tissues. It is unique among glycosaminoglycans in that it is nonsulfated, forms in the plasma membrane instead of the Golgi, and can be very large, with its molecular weight often reaching the millions. One of the chief components of the extracellular matrix, hyaluronan contributes significantly to cell proliferation and migration, and may also be involved in the progression of some malignant tumors.