The hydroisomerization of n-pentane, n-hexane and n-heptane on platinum-hydrogen beta catalysts (Pt/HBEA) was compared with that on platinum-hydrogen mordenite catalysts (Pt/HMOR) of various silica-aluminum ratios at temperatures ranging from 190 to 310 degrees C. For Pt/HMOR, the isomerization yields were found to depend on both the carbon number of feed and the framework Si/Al ratio of HMOR and to be enhanced by exchanging with magnesium ions, while for Pt/HBEA high selectivity of isomerization and conversion were observed. This may be caused by the open structure of tri-dimensional channels in beta zeolite.