Libraries have for hundreds of years been an important entity for every kind of institute, especially in the educational sector. So now it is an age of computers and internet. People are now using electronic resources to fulfill their needs and requirements of their life. Therefore libraries have also converted to computerized systems. People can access and use library resources just sitting at their computers by using the internet. This modern way of running a library has been called or given the name of digital libraries. Digital libraries are getting famous for flexibility of use and because more users can be facilitated at a time. As numbers of users are increasing, some issues relevant to interaction also arise while using digital libraries interface and utilizing its e-resources. In this thesis we evaluate usability factors and issues in digital libraries and the authors have taken as a case study the real time existing system of the digital library in BTH. This thesis report describes digital libraries and how users are being facilitated by them. Usability issues are also discussed relevant to digital libraries. Users have been the main source to evaluate and judge usability issues while interacting and using this digital library. The results obtained showed dis¬satisfaction of users regarding the usability evaluation of BTH:s digital library. The authors used usability evaluation techniques to evaluate functionality and services provided by the BTH digital library system interface. Moreover, based on the results of our case study, suggestions of improvement in BTH:s digital library are presented. Hopefully, these suggestions will help to make BTH digital library system more usable in an efficient and effective manner for users.