Searching databases and subscriptions available online has proven to be the most expedient means for library users to acquire information needed. The library arguably bears such a mission to make available as much information online as possible. However, the cost for a library to upgrade and expand their e-services seems to be rather high, amidst school's limited budget. Relevant ROI studies would apparently be needed to help validate the spending on a library's online digital services. This research conducts the following three ROI assessments to investigate the case relating to Southern Taiwan University Library. First, using a contingent valuation method, a survey done to determine the ROI based on the fees users are willing to pay for e-services. Second, in reference to the service value calculator the Massachusetts Library Association uses, ROI is done based on inter-library loans and usage. Third, using the model of University of Illinois’s study in which e-resources has been proven effective for proposals to secure outside funding, ROI case in point is positive. The conclusion shows the positive economic value for Southern Taiwan University Library to invest on e-resources.