Disclosed are a polysilane monomolecular film and a polysilane built-up film formed by building up a plurality of said monomolecular films, said monomolecular film consisting of a polysilane having a repeating unit represented by general formula (1) given below: ##STR1## where, R.sup.1 represents a substituted or unsubstituted alkyl group having 1 to 24 carbon atoms or a substituted or unsubstituted aryl group having 6 to 24 carbon atoms, R.sup.2 represents a divalent hydrocarbon group having 1 to 4 carbon atoms which can be substituted, and X represents hydroxyl group, amino group, carboxyl group, or a hydrophilic group having at least one selected from the group consisting of hydroxyl group, amino group, carboxyl group, amide linkage, ester linkage, carbamate linkage and carbonate linkage. The polysilane monomolecular film and built-up film can be formed on a substrate by an LB technique. In the films, the molecules of the polysilane having the repeating unit (1), that is, the Si-Si backbones are oriented in a fixed direction.