The microstructure of an 11% Cr martensitic steel was investigated in normalized-andtempered condition. It was found that the microstructure was tempered martensite consisting of prior γ grains and laths. M23C6 precipitates were mainly distributed along prior γ grain boundaries and lath boundaries and small amount of M3B2 particles were aligned almost as a line along rolling direction. MX nano-particles were distributed in the matrix. Complex inclusions containing titanium were also found in the microstructure. Tensile cracks were easily to nucleate at the interface between matrix and M3B2 particles or inclusions.