NOVELTY - Curable composition comprises either: an organic polymer (I) that has less than one hydrolyzable silyl group per molecule on average and contains 5-80 wt.% of oxyethylene units; or 100 parts by weight of an organic polymer (II) having at least one hydrolyzable silyl group per molecule on average, and 5-200 parts by weight of the organic polymer (I).    USE - The curable composition is useful in: waterproof coating material (claimed) for buildings; and architectural and industrial sealants (e.g. architectural elastic sealants, siding board sealants, double glass sealants and vehicle sealants, electric and electronic part materials, and solar cell backside sealants), electrical insulation materials (e.g. insulative coating materials for electric wires and cables), pressure-sensitive adhesives, adhesives, elastic adhesives, contact adhesives, tile adhesives, reactive hot melt adhesives, paints, powder paints, coating materials, foams, sealants for can tops, radiation sheets, potting agents for electrics and electronics, films, gaskets, marine deck caulking, casting materials, various molding materials, artificial marble, rust-proof, waterproof sealants for the edges of wire-reinforced glass and laminated glass, vibration proofing, vibration deadening, sound insulating, and quake-absorbing materials used for vehicles, boats and ships, household appliances, and liquid sealants and waterproof materials used for automobile parts, electric parts and various machinery parts.    ADVANTAGE - The curable composition: has excellent moisture permeability; has easy workability and prevents migration or exudation of a plasticizer to the surface of the cured product; provides waterproof material enabling increase in energy efficiency and durability of buildings and preventing contamination of the indoor air; has high activity and improved curability and storage stability; exhibits excellent restorability, durability, elongation, tensile strength and creep resistance; has high weather resistance, heat resistance; and provides waterproof coating material having high waterproof reliability owing to the seamless coating film without joints and being adaptable to locations with complicated shapes.