The invention relates to an optical waveguide tube comprising a tubular cladding filled with a solid core having a higher refractive index than the cladding. In one form, a resin material having a Tg of up to 50.degree. C. and a modulus of elasticity of up to 10.sup.9 dyne/cm.sup.2 is used as the core. In another form, a copolymer of acrylic acid, methacrylic acid or a lower alcohol ester thereof with a higher alkyl (meth)acrylate is used as the core, preferably in combination with a phosphate, aromatic carboxylate, aliphatic carboxylic acid, aliphatic carboxylate or glycol. In a third form, such an optical waveguide tube is prepared by filling a hollow tubular transparent cladding having opposite open ends with a liquid monomeric charge and causing the monomeric charge to polymerize while pressurizing the exposed surfaces of the monomeric charge inwardly from the opposite open ends along an axial direction of the cladding, thereby forming a core within the cladding.