Cataloguers are library professionals that provide users with critical service(s) through prompt processing of information resources. This affords library users the opportunity to obtain relevant information within a record time. With the influx of information resources in diverse formats, the work of cataloguers becomes challenging which leads to low level of work performance.Toimprove on their performance therefore,it becomes expedient to investigate how mentoring and teamwork could determine the cataloguing personnel work performance in academic libraries in South-West, Nigeria. The research design adopted for this study was survey method with total population of the study consisting of 263 cataloguing personnel in the academic libraries in South-West, Nigeria. The data collection instrument used was a validated questionnaire with a response rate of 98%. Data were analyzed using descriptive mean, standard deviations and inferential simple correlation, Pearson product moment correlation and multiple regression statistic. The result showed that high team effectiveness Ẍ = 44.86 SD 5.57 satisfactory mentoring practice Ẍ = 29.07, SD 4.13 and excellent work performance Ẍ = 33.46 SD 4.81 existed among the cataloguing personnel.The study concluded by establishing that teamwork and mentoring are critical ingredients for improving work performance of cataloguing personnel.  Therefore, there is need for library managers to encourage teamwork and formalize mentoring among cataloguing personnel in order to enhance their work performance.