The study investigated the purposes for staff performance appraisal in Nigerian university libraries. The study adopted a survey method.  The population of the study consisted of forty- two (42) heads of division of libraries. The instrument used for data collection was questionnaire. A total of 42 copies of questionnaire were distributed to the 42 heads of libraries, and all were duly completed and returned. The data generated for the study was analyzed using frequency table and percentage. The findings show that the main purposes for staff performance appraisal in Nigerian university libraries include among others: to identify the strength and weakness of staff, provide feedback on staff performance, to assess potentials for growth, and training and development for staff. Based on the findings, it is recommended that Nigerian university libraries should develop a unique appraisal criteria or guidelines due to the peculiar working conditions and tasks performed by library staff, which differ from other staff in the universities.