Effects of water contained in the sample, the type of sensitizer, and the nature of vinyl monomer on vapor phase photografting on cellulose were investigated at 60°C. The grafting was enhanced by the water contained in the cellulose sample, resulting in an increased percent grafting with increasing the quantity of water. The use of sensitizers such as ferric chloride, ferrous sulfate, ceric ammonium nitrate, hydrogen peroxide, benzophenone, and sodium anthraquinone-2,7-disulfonate led to accelerated graftings. However, the maximum grafting was observed at an optimum quantity of sensitizer for each sensitized system, and the formation of grafted polymer was restricted by the use of sensitizer beyond the quantity. Ferric chloride and hydrogen peroxide exhibited higher activities among the sensitizers. With respect to the nature of monomer, methyl methacrylate, acrylic acid, methacrylic acid, and acrylonitrile were observed to be introduced into cellulose substrate by the vapor phase photografting, though no initiation was recorded for styrene and N-vinylpyrrolidone. However, the latter monomers were introduced by using monomer mixtures with acrylonitrile, affording a maximum percent grafting at a certain monomer composition.