In this study the results of the characterization of hierarchical silica-gel samples with nitrogen adsorption and positron annihilation lifetime spectroscopy (PALS) were compared. The hierarchical silica-gel samples were synthesized by pseudomorphic transformation of a meso porous silica gel with CTAOH. The results of the PALS measurements clearly indicate the hierarchical pore structure of the materials. Two individual pore systems can be detected with a good resolution. The peak area of the signals can be calculated and compared with the pore volumes determined by nitrogen adsorption.