To provide a method for molding a cap for a lemonade bottle, capable of integrally molding a lemonade bottle cap made of a synthetic resin in the state that a glass ball is held.

In the method for molding a cap for a lemonade bottle, a cap main body 22 made of a rigid resin and a ball holding part 21 made of a flexible resin are integrally injection-molded by a two-color injection molding machine. A flexible resin is injected into a cavity for molding the ball holding part in the state that a glass ball 20 is fixed in the cavity, and the ball holding part 21 where the glass ball is held in a closely contact state is molded. After the glass ball 20 and the ball holding part 21 are then transferred to a cavity for molding the cap main body, a rigid resin is injected into the cavity to integrally molding the cap main body 22 on the outer side of the ball holding part 21. Both the ball holding part 21 thus obtained and the glass ball 20 are completely in a closely contact state in the cap for the lemonade bottle.