Abstract: A serum separating sealant having a specific gravity at 20.degree. C. of 1.035 to 1.065, a viscosity of 100 to 400 Pa.S and a yield stress of 100 to 400 dyne/cm.sup.2 and comprising:(A) 100 parts by weight of a polymer having specific gravity at 20.degree. C. of 0.94 to 1.06 and a viscosity of 10 to 140 Pa.S, derived from an alkyl acrylate or alkyl methacrylate monomer having the formula (I): ##STR1## wherein R.sup.1 denotes H or CH.sub.3, R.sup.2 denotes an alkyl group having 1 to 18 carbon atoms;(B) 0.5 to 10 parts by weight of at least one component selected from silica and bentonite; and(C) 0.01 to 2 parts by weight of at least one surfactant selected from the group consisting of:(C-1) fluorocarbon-based surfactants;(C-2) polyester modified alkylpolysiloxane based surfactants.