In this age of information explosion no library is able to satisfy all the needs of its users due to various constraints. It is because of this phenomenon that the concept of library IMS has developed. To achieve this, those who are responsible for the libraries should take into account their active and passive users. Furthermore, not only the academicians who make use of the libraries but also those who do not make use of them should be considered. It is against this background that this study main purpose was to evaluate the effectiveness of the use of opens source Integrated Management Information Systems (MIS) in Libraries, Strathmore University as a case. The objectives of the study were: to determine the effectiveness of open source integrated information management system in use at Strathmore university library, to find out the users’ attitudes towards the integrated management information system at Strathmore University Library’, to find out the challenges facing the integrated management systems in Strathmore university and suggest recommendations that would help in improving the use of Koha at Strathmore University Library. The study utilized a case study and was carried out within Strathmore University. The study found out that the integration of information management system in the provision of library service is to a great degree perceived to be effective. However, there was need for improvement. The findings further revealed that, most members of staff and students have positive attitudes towards the use of Koha at the Strathmore University library. This implies that they would appreciate being trained to use it and support any efforts to improve the system. The study concluded that there were still enormous challenges in integration of the management information system in Libraries due some reasons for instance the constant change of software, internet failure and the lack of technology know how among some clients. The study recommended that there is need for continuous training to students and staff to keep then abreast of the technological changes of integrated information systems and innovative strategies of dealing with the challenges associated with Koha.