The deterioration of cellulosic materials due to the growth of mildew causes enormous loss to us. It is, therefore, necessary to give adequate protectional treatment against mildew spoilage on cellulosic materials. In this study, fourteen chemicals were treated to the strain of Chaetomium globosum A.T.C.C., then phenyl mercuric acetate (P.M.A) was proved to be a most effective fungicide out of various chemicals. Another chemicals, such as Na-pentachlorophenolate, tuget, $alpha$-naphthol, caprylic acid and orthocidc were also proved to be effective mildew-proofing agents.