Tensile tests for many kinds of structural steels containing mild and high tensile steels have been performed in rolling, transverse and thickness direction. From these experimental results we knew that tensile strength exhibits little or no directional properties but ductility decreases markedly in the thickness direction. Moreover, the effect of this directionality on the fracture under combined stresses have been investigated by thin hollow cylindrical test specimens cutted from a thick pressure vessel steel. The causes of their directionality were analyzed experimentally and we concluded that alignment and shape of microscopic inclusions may be main causes of the directionality of hot-rolled structural steels.