The library is the major source of information provider in the university community, which makes it a storehouse of information for intellectual development for staff and students. The effective and efficient performance of any private university library personnel will greatly depend on the work environment of the private university library which can be conducive or unconducive for them to perform their task. To this effect, this study investigated the influence of the work environment on organisational performance of private university libraries in South-west, Nigeria. Two research questions were answered while one hypothesis was tested at 0.05 alpha level. The study adopted survey research design of the correlational type with the study population of 430 librarians from 30 private universities established as at 2021, in the six states of South-west, Nigeria. The study used total enumeration method to cover all the professional and para-professional library personnel. A validated questionnaire was used for data collection. The Cronbach alpha was used to compute the reliability coefficient of the instruments as follows: Work environment (0.730) and organisational performance (0.885). Sample of 378 questionnaires were retrieved and used for data analysis using descriptive statistics, while inferential statistics was used for data analysis. Findings revealed that the state of work environment of private university libraries in the south-west is conducive. Result from the finding indicated that there is large organisational performance in the private university libraries, the result also revealed that there is a significant relationship between work environment and organisational performance of private university libraries in South-West, Nigeria (r=.513, n=378, p (.000)<.05) and Psychological work environment (r=.449, p(.000)<.05), has the highest influence. Hence, work environment influenced/enhanced organisational performance of private university libraries in the study.