Fibrous proteins, also called scleroproteins, are long filamentous protein molecules that form one of the two main classes of tertiary structure protein (the other being globular proteins). Fibrous proteins are only found in animals.

Fibrous proteins form 'rod' or 'wire' -like shapes and are usually structural or storage proteins i.e. the protein is inert. They are practically water-insoluble and are found as an aggregate due to hydrophobic R-groups that stick out of the molecule. The amino acid sequences they are made from often has limited residues with repeats. These can form unusual secondary structures, e.g. collagen triple helix. The structures often contain 'cross-links' between chains, for example cys-cys disulfide bonds between keratin chains.

They are usually used to construct connective tissues, tendons, bone matrix and muscle fibre.

Examples of fibrous proteins include keratins, collagens and elastins.

Protéine fibreuse