The pore structure of porous modified cyclic silsesquioxane (mCSSQ) thin films with different porogen concentration were investigated by means of EP and PALS as a "round robin" experiment. A plausible pore structure and its evolution as a function of porogen concentration (and hence porosity) can be deduced. At low concentration the cyclodextrin-based porogen molecules may be singly dispersed, resulting in isolated pores, while porogen agglomeration and pore collapse become severe with increasing concentration. The porosity increases and pore size distribution become broad with increasing porogen concentration. An interconnected cylinder-like pore shape can be postulated on the basis of the tendency for CD molecules to linearly interact. The dielectric constant and mechanical property of the porous mCSSQ thin films are strongly affected by the film's porosity.