The isomerization of endo-tricyclodecane to adamantane on commercially available zeolites was studied. Zeolites beta, mordenite, Y and ZSM-5 were tested and zeolite Y was the best. The sufficient acidity for the above rearrangement was exhibited by the zeolite in thr hydrogen form. The Si/Al ratio in zeolitic framework influenced also the activity and selectivity of adamantane formation. The optimum reaction temperature was found to be 270 degrees C.