A chemically adsorbed film containing hydrophilic groups is formed on a substrate such that it is chemically bonded by Si covalent bonds to the substrate. The adsorbed film has an improved hydrophilic property. In addition, the film provides an excellently durable and transparent fog-proof substrate. According to the method of the invention, a substrate containing hydrophilic groups is contacted with a non-aqueous solution containing a surface active material having straight chain molecules each having at one end a chlorosilyl group and at the other end at least one functional group selected from the group consisting of a bromo group, iodo group, cyano group, thiocyano group, chlorosilyl group etc. to cause a dehydrochlorination reaction between hydrophilic groups on the substrate surface and chlorosilyl groups of the surface active material, thereby forming a chemically adsorbed film on the substrate surface. The functional group at the other end of the surface active material is converted into at least one hydrophilic group selected from the group consisting of --OH, --COOH, --NH.sub.2, .dbd.NH, --N.sup.+ R.sub.3 X.sup.- (X representing a halogen atom, R represents a lower alkyl group), --NO.sub.2, --SH, and --S).sub.3 H groups.