Three kinds of shape selective reactions were realized over 0.5 wt% Pt M 2.1 H 0.9 PW 12 O 40 (abbreviated as 0.5 wt% Pt–M2.1, M=Cs, Rb, and K) and 1.0 wt% Pt–Rb2.1 catalysts. The adsorption studies of argon, nitrogen, and organic molecules with different molecular sizes revealed that the pore distributions of all the catalysts were unimodal in micropore range and the pore sizes increased with increasing the sizes of alkaline ions. On 0.5 wt% Pt–Cs2.1 (pore width: 0.50 nm), n-butane (molecular size: 0.43 nm) was oxidized more easily than isobutane (0.50 nm). In contrast, both butanes were oxidized at similar rates on 0.5 wt% Pt–Rb2.1 (pore width: 0.60 nm) and 0.5 wt% Pt–K2.1 (larger than 0.60 nm) catalysts. In the hydrogenation of aromatic compounds over the 0.5 wt% Pt–Rb2.1, the high activity ratio of benzene (molecular size: 0.59 nm) to m-xylene (0.64 nm) suggests that reactant shape selectivity occurs due to its pore width. One weight % Pt–Rb2.1 promoted the highly selective skeletal isomerization of n-butane and n-pentane while 0.5 wt% Pt–Cs2.1 did not. The high selectivity of 1 wt% Pt–Rb2.1 is attributed to the pore size, together with the high acid strength estimated by NH 3 -TPD.