Purpose: The paper presents evaluation of the influence of refinement as a result of repeated austenitizing, cooling rate after repeated austenitizing on the morphology of hypereutectoid cementite and fracture toughness of G200CrMoNi4-6-3 cast steel. Moreover, the elimination of hypereutectoid cementite in structure of Widmannstatten type precipitates from the structure of investigated cast steel has been undertaken. Design/methodology/approach: The heat treatment has been planned on the basis of CCT diagram prepared for that cast steel. Basic research of G200CrMoNi4-6-3 cast steel included metallographic analysis and fracture toughness research (impact strength, stress intensity factor K Ic and of course hardness). Findings: The test material has been G200CrMoNi4-6-3 hypereutectoid cast steel. Heat treatment of investigated cast steel allows to refine the grain and eliminate from it's structure the hypereutectoid cementite in structure of Widmannstatten type. At very low cooling rate the precipitates of hypereutectoid cementite become partially coagulated. The study of the influence of cooling rate on the mechanical properties of G200CrMoNi4-6-3 cast steel had proven that elimination of hypereutectoid cementite in structure of Widmannstatten type from the investigated cast steel structure to small degree increases it's fracture toughness. Research limitations/implications: The new heat treatment of G200CrMoNi4-6-3 cast steel. Practical implications: G200CrMoNi4-6-3 cast steel of ledeburite class is used mainly for rolls production. Any data related to the structure and mechanical properties of that cast steel are precious for the manufacturers and users of the mill rolls. Originality/value: The new heat treatment (annealing) and mechanical properties of G200CrMoNi4-6-3 cast steel.