In this study, improvement of fracture toughness and strength of gray cast iron by reinforcing steel fiber was investigated. Three point bend specimens were used to calculate the flexural strength and fracture toughness. Fracture toughness of the reinforced cast iron with two distinct volume fraction (Vf = 0.05 and 0.08) were calculated by compliance method and J-integral method using single specimen technique. The study shows that fiber reinforced composite has higher fracture toughness and flexural strength than cast iron without reinforcement. Also, fracture toughness increases with increasing volume fraction of reinforcement. Optical and scanning electron microcopy (SEM) analyses were used to examine the microstructure and fracture surface. It is noted that the carbon diffuses from gray cast iron to steel fiber and graphite free transition regions with high hardness were observed due to the carbon diffusion.