PURPOSE: To produce an optical fiber having improved orienting property of the clad part of the glass fiber and enhanced mechanical strength by coating the surface of an optical fiber with a curable synthetic resin composite having properties of a liq. crystal after rubbing the optical fiber and curing the composite by irradiation with actinic rays.

CONSTITUTION: A glass fiber 1 formed by drawing a preform 10 in an oven 12 is coated with a layer of a curable synthetic resin composite by means of a fiber clad forming device 14. The layer is cured with radiation from a high pressure mercury lamp 16 and a buffer layer 2 of synthetic rubber is formed. The surface of the optical fiber is then rubbed in the longitudinal direction by passing through velvet cloth 18 and an oligomer having reactive groups and a mol.wt. of ≤5,000 is applied and cured in a temp. range in which the composite has a state of a liq. crystal by irradiation with light from a mercury lamp to form a 2nd synthetic resin layer 3. The resultant optical fiber is further covered with a tubular thermoplastic resin film 4 so that it can freely be moved in the film 4.