糖原（glycogen）又称肝糖、动物淀粉，是人类等动物和真菌储存糖类的主要形式；是多糖的一种，由葡萄糖失水缩合作用而成。主要生物学功能是作为动物和真菌的能量储存物质。

在人体中，糖原主要由肝脏和肌肉的细胞产生与存储，并且作为长期存储的次级能量（还有作为存储的主要能量是在脂肪组织积累的油脂）。肝糖原可以由肝脏细胞和肌肉细胞合成。由肝糖原转化的葡萄糖会给全身各处使用，包括中枢神经系统。

在肝脏细胞（肝细胞），糖原可以在饭后不久构成高达其鲜重（成年人100-120克）的8％。只有储存在肝脏的糖原可以由其他器官使用。在肌肉，糖原的浓度较低（约肌肉质量的1-2％）。人体主要储存在肝脏、肌肉和红血球。

Glycogen is a multibranched polysaccharide of glucose that serves as a form of energy storage in animals and fungi. The polysaccharide structure represents the main storage form of glucose in the body.

In humans, glycogen is made and stored primarily in the cells of the liver and the muscles hydrated with three or four parts of water. Glycogen functions as the secondary long-term energy storage, with the primary energy stores being fats held in adipose tissue. Muscle glycogen is converted into glucose by muscle cells, and liver glycogen converts to glucose for use throughout the body including the central nervous system.