Two 0.1wt% Pt-porous glass catalysts have been characterized: mesopores formed by finely dispersed colloidal silica inside a macroporous glass, and micropores defined by the porous glass itself. Introducing the so-called range order length parameter L, chord length analysis for L = 5 nm yields specific structure parameters of the metal particles inside both catalyst supports ( dispersion, specific metal surface areas, basic arrangement, size distribution and volume fraction). The pore size available basically differs with both pore systems. In the one case an unlimited three-dimensional growth, and, in the other one a limited two-dimensional growth of small Pt-crystallites have been detected. The corresponding particle size distributions f(d) and f(H) have been determined.