To provide a composition with a small thickness to be placed in a gas sorbing device, for sorption of both a residual gas in an evacuated chamber and impurities in an inert gas, which can be stored and transported without being kept under an inert atmosphere after production of a mixture.

The device is provided with a composition for gas sorption comprising a gas sorbing component A dispersed in a cross-linked porous matrix. The composition is produced by a process comprising: a step of mixing and dispersing at least one precursor into a matrix containing a polysiloxane resin, wherein the precursor can be converted into the gas sorbing component A through the following heat treatment, and the polysiloxane resin is resistant in a continuous treatment at a temperature up to 650C when filled with an inorganic material; and a step of subjecting the thus obtained mixture to a heat treatment under vacuum or an atmosphere of a gas inert to the component A under a condition such that the precursor is converted into the gas sorbing component A and the cross-linked structure of the polysiloxane resin is retained.