Job burnout is an important aspect of organisational behaviour that has negative impact on librarians and organisational outcome. Despite the efforts made by library management to prevent job burnout among librarians, high level of emotional exhaustion, cynicism and inefficacy remain a major challenge. Poor response to job burnout by librarians’ may be attributed to inability to exhibit citizenship behaviour in the library. The study investigated the influence of organisational citizenship behaviour on job burnout among librarians in university libraries in Nigeria. The study employed survey research design. The population of the study consisted of 624 librarians from 38 public universities in Southern Nigeria. Total enumeration was used. Data were analyzed using descriptive and inferential (simple and multiple regression) statistics. The findings revealed that organisational citizenship behaviour significantly influenced job burnout of librarians in university libraries in Nigeria (β = .252, t(498) = 5.815, R2 = .063, p < .05). There was a low level of job burnout among librarians (M = 2.20, SD = 1.33 on a scale of six) and librarians exhibited organisational citizenship behaviour to a certain degree (M = 2.95, SD = 1.00 on a scale of five). The study concluded that organisational citizenship behaviour contribute to low level of job burnout among librarians in universities in Nigeria. The study recommended that in order for librarians to continue to perform optimally, library management should maintain the current work atmosphere together with ensuring improvement to sustain the low level of job burnout among librarians.