This study investigated the job satisfaction factors influencing the job satisfaction of librarians in Federal and State University libraries in Southern Nigeria. Job satisfaction is an important concept that can affect labor market behavior as it has a great influence on job-related behaviors such as productivity, work effort, absenteeism, turnover rates, and employee relations. The study adopted the survey research design. The population was made up of 500 librarians in thirty seven federal and state university libraries in Southern Nigeria. Sampling was enumeration as all members of the population were given the opportunity to participate. A questionnaire was used for data collection and was analyzed using percentages, standard deviation, and mean. Among other factors indentified, it was shown that job security, satisfactory relationship with my supervisor, satisfactory interaction with colleagues and satisfactory interaction with information user/customer/ clients were significant factors that influenced the librarians’ job satisfaction. However, satisfaction with salary and fringe benefits, working condition, and opportunities to conduct research were rated low which signifies that the librarians are not satisfied with these job satisfaction facets. Based on this, recommendations such as library administrators considering improving the salary levels and the fringe benefits of the librarians, improving their working conditions; and granting the librarians opportunities to conduct research were made.