The present invention relates to a mixing system comprising a vessel (1) for housing a disposable fluid mixing bag (2), which vessel (1) comprises a base (3) supporting the fluid mixing bag (2) and a sidewall (4) extending vertically upwards from the base (3). The sidewall (4) of the vessel comprises a door opening (5) which is closable by a sliding door (6). The system with the sliding door provides an easy access to the inside of the vessel (1) in a space saving manner.