Librarianship as a profession engages in mentoring in order to sharpen and sustain professional practice and be abreast with new development on the job. The study is on mentoring for professional development of librarians in Nigerian university libraries. This present study is a survey of 250 professional librarians from Nigerian university libraries. Questionnaire was used to collect data from the respondents. The percentages of the responses were tabulated. The findings showed that mentoring programmes through which librarians are mostly mentored are sponsorship to conferences, seminars and workshops and individual mentoring. Mentoring is beneficial to academic librarians in that it equips young librarians for more challenging tasks ahead of them. Mentors use the opportunity to gradually handover to younger librarians. The study also revealed that non availability of facilities required for the mentorship and lack of awareness on the need to mentor subordinates are the major problems associated with mentoring of academic librarians in Nigerian university libraries. The following recommendations were made based on the findings, that adequate facilities should be provided by the heads of university libraries to make the job of both mentor and mentee easy; and parent institutions should be willing to release funds to libraries for the procurement of facilities.