To provide a contents mixing cap which can be operated easily, stores one content separated from the other content until they are used, and can mix both contents when they are used.

This relates to a contents mixing cap 100 to be mounted on the opening of a container main body, and the cap comprises a cap main body 110 whose inner peripheral face is formed with a fitting part 28 to be mounted on the opening of the container main body and which is provided with a tube 24 for storing one content having a thin closed bottom 26 able to be cut open and hanging down from the bottom face of a top wall 20, a cut off tube 120 which closes a head part 32, is formed with a flange 34 around the outer periphery of the head part and is fitted in the tube 24 fluid tight and swingably, and a roughly U shaped stopper 130 positioned between the flange 34 of the tube 120 and the top wall 20 of the cap main body 110.