The invention provides a silicone monomer which is suitable for the manufacture of ophthalmic devices, such as contact lenses, intraocular lenses, and keratoprosthesis, a monomer composition containing the monomer, and a polymer which fulfills both surface hydrophilicity and oxygen permeability at the same time. The silicone monomer of the present invention is represented by the formula (1a) or (1b):(X: a monovalent C2 to C6 organic group having one or more -OH and optionally one O or N in its main chain Z1 to Z9: a C1 to C4 alkyl group n: 1 to 3 a and b: 0 or 1).
