<p>A mold additive for use in the continuous casting is disclosed, which comprises a base material for slag having a chemical composition of CaO-SiO2-A?2O3 system, a flux and a carbonaceous aggregate. The mold additive contains 0.5-2.0% by weight of carbon black and 1-4% by weight of activated carbon with an average particle size of not more than 10 .mu.m as the carbonaceous aggregate, and has a bulk density of not more than 0.9 g/cm3.</p>
