OBJECTIVE： To provide evidence support for the economic benefits of generic drugs as substitutes for original drugs， and to provide suggestions for promoting the use of generic drugs. METHODS： Twelve kinds of drugs with both original and generic versions for treating hypertension and diabetes were selected from a tertiary public hospital in Jiangsu province. The proportion of usage quantity， the ratio of amount， price ratio were analyzed quarterly during 2017-2018. RESULTS： From the first quarter of 2017 to the fourth quarter of 2018， the ratio of quantity of original drugs increased from 24.53％ to 39.12％， while that of generic drugs decreased from 75.47％ to 60.88％； the ratio of amount of original drugs increased from 39.45％ to 61.47％， while that of generic drugs decreased from 60.55％ to 38.53％； the price ratio of generic drug to original drug decreased from 0.50 to 0.40. With the same efficacy， the cost of generic drugs replacing original drugs in 2018 could save 622，100 yuan， and the cost savings rate could be 47.65％. CONCLUSIONS： Drug expenditure could be reduced by substituting original drug with generics， but the useage quantity and amount ratio of generic drug in this hospital is gradually declining. So， in order to save drug experditure， it is necessary to speed up the process of conformity evaluation and clinical equivalence study of generic drugs， increase the education and publicity of generic prescriptions and rational use， so as to improve doctors’ and patients’ recognition of the quality and efficacy of generic drugs， cooperate with the centralized procurement policy to encourage the purchase and use of generic drugs.