Abstract: Present invention provides a photosensitive and high energy beam sensitive resin composition which may be used as a resist material for forming both of the positive and negative patterns. The resin composition comprises: a substituted polysiloxane having the main polysiloxane chain and a substituent hydrophilic group or groups; and a solvent for the substituted polysiloxane. The substituted polysiloxane used in preferred embodiments of the invention are produced by acylating polysiloxanes including polydiphenylsiloxane and polyphenylsilsesquioxane to introduce acyl groups, followed by oxidation of the thus introduced acyl groups to convert them into carboxyl groups or by reducing the thus introduced acyl groups to convert them into alpha-hydroxyalkyl groups. The acyl, carboxyl or alpha-hydroxyalkyl groups are further substituted to obtain substituted polysiloxanes which are soluble in an aqueous alkali.