Purpose: The study sought to investigate factors that affect the adoption and use of open access in Tanzanian health sciences universities. Design/methodology/approach: Based on a cross-sectional questionnaire survey, 415 faculty members were selected through a stratified random sampling from a population of 679 in all eight health sciences universities in Tanzania. The response rate was 71.1%. Findings: Based on the social exchange theory (SET), and the Unified Theory of Acceptance and Use of Technology (UTAUT), the study developed a model suitable for assessing open access adoption and usage in academic institutions. The study found that facilitating conditions, extrinsic benefits (professional recognition), behavioural intention and individual characteristics (professional rank, technical skills and number of publications) predicted actual usage of open access. Other factors related to contextual factors (attitude, and open access culture), and extrinsic benefits (academic reward, accessibility and preservation) determined behavioural intention to use open access. Fear to violate publisher’s copyright policies and effort expectancy however de-motivated faculty to adopt open access, while copyright concerns inhibited faculty’s actual usage of open access. Originality/value: This is a first comprehensive study focusing on the health sciences faculty’s open access adoption and usage behaviour in Africa, and Tanzania in particular, and reveals findings that are useful for planning and implementing open access initiatives in other institutions with similar conditions