A joint structure of a composite bicycle frame includes a base layer and at least one reinforcing layer. The base layer is made of a first polymeric matrix material doped with a plurality of first fibers. The first fibers have random fiber orientation, and the base layer has a first thickness. The reinforcing layer is adhesively connected to the base layer. The reinforcing layer is made of a second polymeric matrix material doped with a plurality of second fibers. The second fibers have a single fiber orientation. The reinforcing layer has a second thickness which is smaller than the first thickness of the base layer.