Abstract: A cap assembly releasing dose upon opening is mounted to a bottle to perform a container with two doses mixing upon opening. The cap assembly comprises a collar and a cap. The collar has an engaging recess, an inner threaded section defined at an opening of the engaging recess, a sealing surface defined at a bottom of the engaging recess, and multiple passages formed between the sealing surface and the inner threaded. The cap has a filling space, a cap opening communicated with the filling space to combine with the sealing surface, and an outer threaded section defined on an outer periphery of the cap opening to engage with the inner threaded section of the collar. Because the cap assembly has a simple structure, the cap assembly with the container is fully assembled by automatic operation to be made store two doses in a cost-effective way.