Abstract: An anaerobic curable sealant composition is disclosed which is suitable as a fluid gasket for use in portions to be sealed in the field of automobile parts for example and which is superior in oil resistance and flexibility, the flexibility being retained even in a high-temperature atmosphere. The composition is prepared by adding core-shell fine particles consisting of a core of a rubbery polymer and a shell of a glassy polymer to an anaerobic curable sealant comprising a urethane (meth)acrylate prepolymer, a radical-polymerizable monomer and an organic peroxide. It has a repulsive force high enough to retain flexibility and sealability capable of coping with vibrations and external stresses induced in a seal portion and is superior in oily surface adhesion.