Longitudinal cracking when continuous casting of peritectic steels was studied in this work. Dependency of slab scarfing volume and surface cracking on the steel chemical composition was investigated. The optimum casting speed and taper parameter of the mold were determined based on analytical modeling and statistical analysis of surface cracks observed in industrial billets. It was shown that longitudinal cracks on peritectic slabs could be reduced when the Mn to S ratio was kept above ~150. Such surface defects were decreased to 30-35 % by optimizing the steel composition, melt temperature and casting speed. Also by using an optimum taper of the mold the scarfing volume was reduced to 32-36 %.