PURPOSE: To improve the hydrophilicity of a contact lens surface further to improve the feel of mounting and wearing and to impart functions of properties to prevent contamination, to prevent dislodgment, etc., to the lens by subjecting the lens to a surface treatment with the surface treating liquid for contact contg. specific compds.

CONSTITUTION: This surface treating liquid for contact lenses contains the compds. expressed by formula. In the formula, R1 denotes a hydrogen atom, methyl group or ethyl group; R2, R3, R4 and R5 are the same or different groups and denote hydrogen atoms or methyl groups; R6 denotes a hydrogen atom or 1 to 20C alkyl group; (p) and (q) denote an integer from 0 to 3 (where p+q=3); (m) denotes an integer from 0 to 100; (n) denotes an integer from 1 to 1000. The contact lens which can be subjected to the surface treatment by this surface treating liquid may be either a soft contact lens or hard contact lens and is more preferably a contact lens consisting of a blank material having functional groups capable of making condensation reaction with alkoxysilane groups, etc., on its surface.