The present invention relates to a catalyst for preparing a lactone, which is prepared by supporting a cupric compound, a zinc compound and at least one alkaline earth metal compound on the supporter. The present invention also relates to a method for preparing a lactone, which comprises a dehydrocyclization reaction of a diol under a gas phase in the presence of the aforementioned catalyst after activating said catalyst. The catalyst for preparing lactone of the present invention is quite economic because of its high activity, long lifetime and high selectivity of products.