To provide a sheet substrate having excellent adhesiveness to metals.

This sheet substrate, such as sheet, film or nonwoven fabric, comprising a liquid-crystalline aromatic polyester such as a wholly aromatic polyester, a wholly aromatic polyesteramide or a semi-aromatic polyester is characterized in that the substrate is sulfonated, for example, with fuming sulfuric acid, chlorosulfuric acid, sulfuryl chloride, sulfur dioxide, or a complex comprising sulfuric anhydride and an electron-donating compound.