A reaction chamber for a chemical vapor apparatus is disclosed. The reaction chamber for the chemical vapor apparatus comprises a housing including an internal space and a susceptor disposed in the internal space so that a substrate is loaded on an upper surface of the susceptor. A shower head is disposed above the susceptor in the internal space of the housing to spray process gas towards the substrate side. An inner barrel with open top and bottom is placed inside the internal space of the reaction chamber so that an upper edge of the barrel is positioned near the showerhead to enclose the substrate and the susceptor. A driving part is connected to the inner barrel. When it is needed to replace the susceptor and the substrate, the inner barrel is changed into an open state in which the substrate and the susceptor disposed in the inner barrel are exposed to the outside of the inner barrel by an operation of the driving part. The inside of the reaction chamber for the chemical vapor apparatus is always closed and thus the reaction chamber is capable of easily replacing a substrate or a susceptor while the vacuum in the reaction chamber is still maintained.