Effect of porosity on mechanical and hygric properties of high performance concrete (HPC) with natural pozzolan as partial Portland cement replacement up to 40% is studied in the paper. The reference HPC mixture is researched as well in order to evaluate the influence of pozzolan usage on concrete performance. For the studied materials, measurement of compressive strength, sorptivity, apparent moisture diffusivity, and water vapor diffusion permeability is done. The obtained data shows that application of the pozzolan as partial cement replacement leads to increase of concrete porosity that is related to the lower mechanical strength and higher moisture transport properties. Therefore, the applied natural pozzolan has a potential to replace a part of Portland cement in concrete manufacturing but its content in concrete mixture has strict limitations.