Interlibrary Loan (ILL) is the sharing of materials among libraries across town or across the globe. User satisfaction and service quality measurement helps us understand how library patrons have used the service and how they perceive the value of the service. The objective of this study is to compare the expected and perceived service levels from the ILL users' perspective in order to ascertain the current service gap and to make improvement. A model of service quality assessment was developed for ILL service based on three focus group interviews. The measurement comprises 20 questionnaire items that represent three dimensions: service interface, content provision, and service performance of the librarian. The survey was administered to the patrons of a university library and 561 usable responses were analyzed. The result showed that 41.9% of the respondents had used ILL within a year. For those who had used the service, the average expected service level was 4.26 by a five-point Likert scale, while the perceived service level was 3.91. This shows that users did consider ILL as important, but the current service requires improvement to fully satisfy them. The study also reveals what aspects of that university's ILL service needed improvement.