A closed isobaric dispenser for carbonated liquid which is affixed to a capped opening of a carbonated liquid containing bottle or liquid holder in airtight manner. The dispenser includes a container, a connecting adaptor and a cap opener. The interior space of the container defines an airtight closed chamber. The container has an inlet opening for the carbonated liquid flowing from the bottle or holder into the airtight closed chamber, and an outlet access for dispensing the carbonated liquid within the container. The outlet access, for dispensing of the carbonated liquid within the container, is secured with a detachable sealing means in airtight manner. The container is adapted to be firmly secured to the carbonated liquid containing bottle or holder by means of the connecting adaptor in airtight manner, wherein the cap is positioned inside the container. The cap opener is disposed coaxially with the holder cap within the airtight closed chamber and comprises a cap sleeve which is adapted to engage with the cap, so that by rotating an operating handle attached to the cap sleeve, the cap is driven to rotate simultaneously so as to unscrew the cap apart from the holder. Since the dispensation or consumption of carbonated liquid is carried out in the airtight closed chamber, carbon dioxide content in the carbonated liquid may not escape to the surrounding atmosphere. Thus the compressed carbon dioxide can be virtually preserved regardless the number of times of dispensation.