A transmission belt includes a belt body, two spaced-apart mounting axles and a reinforcing unit. The belt body forms a loop that defines an inner space. The mounting axles and the reinforcing unit are embedded in the belt body. The reinforcing unit includes at least one cord that includes a plurality of winding segments and a plurality of connecting segments. The winding segments alternately extend around the mounting axles. Each of the connecting segments interconnects a corresponding pair of the winding segments that respectively extend around the mounting axles.