Text in English / The study investigated the usage of Open Access Institutional Repositories (OAIR) in university libraries in Ghana to develop a strategy on how the usage of OAIR in university libraries in Ghana may be enhanced. The study adopted the Technology Acceptance Model (TAM), which was then modified to fit the study. Accessibility, availability and visibility were proposed in addition to the conventional variables of TAM to improve the fit between the data and the theoretical model. Pragmatism paradigm, mixed methods research approach and convergent parallel mixed method design (survey and case study designs) was used for the study. Simple random sampling, stratified random sampling, purposive sampling techniques and the sample size converter were the sampling procedures and methods employed. A total of nine hundred and ninety-eight (998) respondents completed the questionnaires distributed, but for the qualitative phase twelve (12) OAIR managers were purposively selected. The questionnaire and interview guide were used as research instruments to gather relevant data for the study. Descriptive statistics (frequencies, percentages, means and standard deviation) and inferential statistics (multinomial logistic regression and CFA using SEM) were used as statistical tools to analyse quantitative data and thematic analysis was used to analyse qualitative data. The study revealed that there was a low level of OAIR usage in universities among academic staff, notwithstanding the high level of understanding of OAIR. This was evident in the number of research work uploaded onto the OAIR by the OAIR team. Inadequate advocacy, ICT connectivity, infrastructure, funding, power supply, insufficient technological skills, institutional repository policy, absence of incentives, institutional culture and politics and copyright issues were the challenges facing the usage of OAIR in university libraries in Ghana. The study concluded that advocacy, policies, software and staffing enshrined in an institutional guideline on OAIR would enhance OAIR usage. The study developed an OAIR Usage Model and OAIR User Manual, which would be very instrumental in the usage of OAIR in university libraries in Ghana. The model will enhance user satisfaction and intention to reuse the OAIR and making OAIR research outputs available, accessible and visible. The manual specifies the contents and documentsaccepted by the OAIR and ensuring the quality of documents archived. / Information Science / D. Litt. et Phil. (Information Science)