To provide a method of simply and promptly screening the strains that has high-speed cellulose production or can produce the cellulose of high molecular weight from a plurality of specimens.

The objective method of screening the mutant strains of cellulose-producing microorganisms characteristically comprises the step where a microorganism capable of producing cellulose is cultured, the step where a plurality of lots of the cultured microorganisms are subjected to mutagenic treatment to obtain a plurality of mutant strains, the step where the resultant mutant strains are individually subjected to solid culture using a culture medium including water-soluble cellulose ester, mono- or di-saccharides and nitrogen source, the step where the proliferated colonies of the individual mutants are selected on the basis of the differences of properties as standards for strain selection. Thus, bacterial cellulose is obtained by this method.