A filter composed of a mesh structure substrate having deposited thereon and therein activated carbon fiber treated with an alkali and having a length within the range of from 5 to 1,000.mu., wherein the mesh structure substrate has an average cell diameter 3 to 100 times the length of the activated carbon fiber, wherein the activated carbon fiber is adhered to the substrate by a binder, and wherein the activated carbon fiber is deposited on and in the substrate by impregnating the substrate with a dispersion obtained by dispersing activated carbon fiber in a dispersion or solution of a binder, and drying methods for forming and using the same are also disclosed.