Amylopectin is a polysaccharide with a varying structure; It is composed of linearly linked alpha 1,4 linked glucose units (coiled into tubular sections) with occasional alpha 1-6 glycosidic bonds which provide branching points. Each amylopectin molecule may contain 100,000-200,000 glucose units, and each branch is about 20 or 30 glucose units in length, so that these molecules are bushy and nearly spherical in shape.

The many exposed ends can have more glucose units added to them by enzyme action for storage purposes or removed from them for use in respiration.

Amylopectin is one fraction of starch (typicaly 80-90%), the other fraction being amylose (10-20%). Glycogen ("animal starch"), found in the liver and muscles, is effectively similar in structure to amylopectin, but it has shorter branches: 8-12 glucose units.