Positronium-annihilation lifetime spectroscopy (PALS) with an energy-variable pulsed positron beam is used to measure pore size and pore interconnectivity in porous methyl-silsesquioxane (MSQ) films with periodic pore structures. The results obtained for the films with different k values (1.9-2.3) suggest that with increasing porosity the pore structure changes from isolated spheres to connected long cylinders. Comparison between the pore sizes obtained by PALS and TEM is also presented.