The present invention relates to a solid medium containing as a medium-solidifying component a cellulose gel, in particular a cellulose gel which is a porous cellulose gel structure containing cellulose as the skeletal part and having a cellulose concentration of 0.01% or higher and a porosity of 50% or higher, as well as a process for producing the same. The solid medium of the invention can be obtained by dispersing cellulose in a solvent, especially an aqueous thiocyanate salt solution, stirring and/or heating the dispersion to dissolve the cellulose, subsequently cooling the solution and/or removing the solvent to cause the solution to gel, and permeating nutrients into the resultant cellulose gel. The solid medium usable under a wide range of culture conditions where conventional solid media such as agar medium cannot be used, as well as a method for producing the same is provided.