This study investigated librarians' perceptions of the sustainability of Open Source Software (OSS) for library automation in academic libraries in Adamawa State, Nigeria. A descriptive research design was employed. The population comprised 103 librarians from six tertiary institutions, selected through a census sampling technique. Data were collected using a structured questionnaire titled : Perception of Librarians on Sustainability of Open Source Software Questionnaire (PSOSSQ). Mean and standard deviation were used to answer research questions, while ANOVA tested hypotheses at a 0.05 significance level. Findings revealed that librarians generally support OSS adoption, citing improvements in library operations. There were no significant differences in mean ratings across institutions regarding perceptions of OSS
adoption, reasons for its use, or sustainability (p > 0.05). Key benefits identified included free licensing, multiple installations, community support, and system integration. Perceived sustainability was linked to collective decision-making, training opportunities, written procedures, and periodic evaluations. Challenges included lack of training, insufficient technical staff, poor ICT infrastructure, unstable power supply, and inadequate funding.
Suggested sustainability measures included regular training, institutional-industry partnerships, consistent software updates, technical support, and improved funding. The study
concluded that OSS offers cost-effective and flexible solutions for library automation. However, its sustainability depends on institutions investing in technical training, reliable
infrastructure, and supportive policies. This implies that successful OSS adoption requires not just installation but an ecosystem of support that addresses human, financial, and operational gaps. It is therefore recommended that library management develop structured training programmes, build institutional-industry partnerships, and allocate sustainable funding to ensure long-term success.