This study investigated the status and challenges of developing institutional repositories in Nigerian university libraries and the influence on their rankings. It adopted a survey research design carried out in South-East Nigeria. Twenty three universities comprising of 10 publicly funded universities and 13 funded by private and faith-based organizations. Instrument for data collections were structured questionnaire, interview, and analysis of relevant websites. Findings showed among others that the universities were at different levels of implementation of IR; only 26 % of the universities have fully implemented IR. Majority of the libraries lack ICT infrastructure and skilled staff for adoption of institutional repositories; and D-Space is most popular software used. The study also revealed that universities with functional repositories have better ranking nationally and globally.