Abstract: A dehydrogenating catalyst for saturated hydrocarbons comprising platinum, tin, sodium and .tau.-alumina. The support of the catalyst is a large pore diameter .tau.-Al.sub.2 O.sub.3 with dual pore diameter distribution. At least 40% of the total pore volume is contributed by pores with pore diameter in the range of 1000-10000 .ANG.. Platinum, tin, and sodium are impregnated onto support by co-impregnation method, followed by drying, calcinating, and steam-treating, as well as reducing by hydrogen, to prepare a long life dehydrogenating catalyst.