In copper continuous casting, the soot, which is the incomplete pyrolitic product of acetylene, has been used as a mold coat. In this work, under constant acetylene pressure, the characteristics of soot and the optimum condition of sooting were investigated with different acetylene and oxygen flow rate. The soot particles deposited on the mold surface had mainly spherical shape and their sizes were about 20㎚. After reaction with melt, their shapes were changed into polygonal type due to the graphitization. With increasing oxygen flow rate up to 0.6ℓ/min, the amount of residues of soot after heat treatment were kept nearly constant. But the amount of residues increased rapidly with further increasing oxygen flow rate. Degree of graphitization was maximum at 0.4ℓ/min and 5ℓ/min of oxygen and acetylene flow rate, respectively.