NOVELTY - UV absorbent comprises substituted 4-benzylidene-pyrazolidine-3,5-dione (I) or substituted 3,5-dioxo-4-(1-phenyl-meth-ylidene)-pyrazolidine-1-carboxylic acid (II).    USE - The UV absorbent useful in a polymer material (all claimed). The polymer material is useful in polymeric molded products (e.g. plastic, containers, coatings, coated films, fibers and construction materials), in applications for protection of products sensitive to UV light (e.g. filter, packaging material, containers, coating, coated film, ink, fiber, construction material, recording medium, image display device and solar cell cover), paint and also in applications for prevention of decomposition of photo-sensitive compounds. (I) and (II) can protect UV-sensitive organic materials, especially human and animal skins and hairs, from the damaging action by UV irradiation and is thus favorable as a photo protecting agent for use in cosmetic products and pharmaceutical preparations for human and animals.    ADVANTAGE - The polymer material obtained from the UV absorbent is excellent in production suitability when kneaded the UV absorbent with the polymer or dissolved the UV absorbent in a solvent, where the material: causes neither precipitation of the UV absorbent nor the bleed-out owing to a long-term use; is not colored by the UV absorbent; and is excellent in both long-wavelength ultraviolet absorption capacity and light fastness (ultraviolet light fastness), while maintaining the absorption capacity for a long period of time.    DETAILED DESCRIPTION - UV absorbent, comprises substituted 4-benzylidene-pyrazolidine-3,5-dione of formula (I) or substituted 3,5-dioxo-4-(1-phenyl-meth-ylidene)-pyrazolidine-1-carboxylic acid of formula (II).    R11, R12, R14, = monovalent substituent;    R13 = H or substituent having Hammett substituent constant sigma p of -0.35 or more;    R21 = 1-18C alkyl or phenyl (optionally substituted);    R22 = 1-18C alkyl (optionally substituted);    R23 = H, substituent having Hammett substituent constant sigma p of -0.35 or more, or 1-18C alkoxy (optionally substituted);    R24 = monovalent substituent; and    n, m = 0-4.    INDEPENDENT CLAIMS are included for:    (1) substituted 3,5-dioxo-4-(1-phenyl-meth-ylidene)-pyrazolidine-1-carboxylic acid (II); and    (2) a polymer material comprising the UV absorbent and at least one kind of polymer substance.