This study investigates the impact of library resource usage on knowledge acquisition among students in public secondary schools in Arusha City. A convergent mixed-methods design was employed, targeting Form 3 and Form 4 students, teachers, librarians, and school heads. A total of 98 respondents were selected using simple random, stratified, and purposive sampling techniques, including 50 students, 40 teachers, 4 librarians, and 4 school heads. Data were collected through questionnaires, observation checklists, and interviews. The validity of the instruments was ensured through expert review and reliability was tested using Cronbach’s alpha. Descriptive statistics, including mean scores, percentages, and frequencies, were used to analyse quantitative data, while qualitative data were analyzed thematically. The study revealed that the condition of library resources in most public secondary schools was deplorable, with most libraries lacking up-to-date books. It was also found that the use of library resources positively influenced students' knowledge acquisition. The study recommends that the government and education stakeholders should invest in improving school libraries by ensuring access to adequate and current resources. Additionally, it suggests that students be actively encouraged to utilize library resources to enhance their learning and broaden their knowledge base.