This study is to evaluate whether economies of scale exist in four categories of university libraries in the Korea. Regression analysis is used to fit a log-log equation to the total budget-output (total circulation, interlibrary lending and borrowing, reference transactions, hours opened, volumes added, automation and information indicator) for all the types of libraries. In results of the analysis, returns to scale are almost constant in the national and public libraries and larger libraries. But there is presence of economics of scale in private libraries and all of the libraries. Except for hours opened, economies of scale decrease more rapidly.