Effect of normalizing temperature on the microstructure and mechanical properties of a martensitic heat resistant steel with high contents of silicon, chromium and carbon was investigated. It was found that carbides in the steel dissolved greatly above 980℃, additional expansion occurred on the thermal dilation curve and two forms of Cr₂₃C₆ were decorated along the lath boundaries after tempering. When normalized at 1030-1100℃, large size Cr₂₃C₆ carbides containing silicon precipitated along the grain boundaries. Tensile properties of the steel increased with normalizing temperature below 1030℃ and kept almost unchanged at higher normalizing temperatures. The toughness of the steel decreased with normalizing temperature and the large size chain-like Cr₂₃C₆ carbides along grain boundaries were the key factor to reduce the toughness.