The anisotropy of microstructures and mechanical properies in commercial American Petroleum Institute (API) X100 pipeline steel was systematically invesigated by experimental measurements. The experimental results show that anisotropy of yield strength could be observed considerably, which should be attributed to the crystallographic textures due to deformation and transformation of texture components. This is because the effect of the inhomogeneity of microstructure in different directions on the mechanical properties could be reasonably neglected based on the experimental investigation of grain size distribution. The effect of crystallographic texture on the anisotropy of yield strength was interpreted theoretically based on the relationship between yield strength and average orientation factor.