Abstract: A mold additive for use in continuous casting, which includes a base material having a chemical composition of CaO--BaO--SiO.sub.2 --F system, and contains 2-15% by weight in total of at least one carbonate of alkali and alkaline earth metals, 2-30% by weight in total of at least one fluoride of alkali and alkaline earth metals and 0.2-10% by weight of carbon, and, if necessary, 2-10% by weight in total of at least one oxide of Fe, Mn and Ni, and has a solidification temperature of not more than 900.degree. C. and a viscosity at 1,300.degree. C. of not more than 3 poises. The base material has a weight ratio of (CaO+BaO)/SiO.sub.2 of 0.6-2.5 and contains not less than 2% by weight of BaO and 2-15% by weight of F.