Institutional repositories have risen to prominence in the worldwide push towards a knowledge community, serving as a key medium for education, research, and training. In the Sri Lankan environment, institutional repositories are becoming increasingly popular in the digital age. Despite the fact that the country has made significant investments in the development of innovative information and communication technology (ICT) products for education, in particular, the adoption and use of institutional repositories provide a number of obstacles, including issues of accessibility, dependability, copy rights, and so on. The purpose of this research is to examine academic staff awareness and attitudes regarding the usage of institutional repository at the Eastern University in Sri Lanka (EUSL). The survey approach was used; data was obtained by an online questionnaire and analyzed using the SPSS statistical software package. It was determined whether academic personnel were aware or had negative attitudes towards using institutional repository through the use of the Diffusion of Innovation (DOI) and the theory of reasoned action (TRA) theoretical models. According to the data, academic staff members have a high level of understanding concerning institutional repository. The findings suggested that academic staff did not deposit their research work into institutional repository on a regular basis since the vast majority of them were not aware of how to deposit their work into the repository. A recommendation from the study’s conclusion is that libraries should provide appropriate awareness programs and training to researchers about the benefits of using institutional repositories, self-archive publishing, as well as encourage them to deposit their research work in these venues. Finally, it was discovered that the level of awareness and attitude toward institutional repository are both important factors in determining its use.