The present invention discloses an endodontic sealer which comprises a urethane-monoacrylate oligomer, a diluting monomer, at least one photo-initiator, at least one thermal-initiator, and a filler, wherein the urethane-monoacrylate oligomer is obtained by firstly reacting the acrylate with the diisocyanate to form an intermediate with only one isocyanate group, and then reacting the intermediate with the polyol to form the desired urethane-monoacrylate oligomer.