This study seeks to describe and analyze the challenges occasioned by brain drain or human capital flight of librarians on service delivery in Nigerian Universities. The research adopted a descriptive survey design. A purposive sampling technique was used to select two geopolitical zones (South-South and SouthWest) from the six geopolitical zones of Nigeria. Total enumeration was used because the population under study was considered appropriate for the research. The instrument used for data collection was questionnaire. Sixty copies of the instrument were distributed to 60 librarians in the two selected geopolitical zones. Copies of all the questionnaires were completed, retrieved, and found usable, thus giving a response rate of 100%. Survey results indicated that 315 librarians emigrated to foreign lands for various reasons, including unstable academic calendar and prospects for further training among others. This loss of personnel in the university libraries has a negative impact on service delivery as qualified information professionals and Information and Communication Technology (ICT) experts are limited to mentor the younger professionals. Shift duties in academic libraries are also scaled down for lack of manpower. Based on the findings, the researchers recommend that the Federal Government of Nigeria should, as a matter of urgency, robustly fund tertiary education to enhance productivity. As they do this, the National Universities Commission (NUC) is to empower academic libraries by ensuring that the staff development policy is strictly adhered to. This will translate into self-enhancement for staff, positive job attitude, and retention of professionals in the system. Keywords brain drain, human capital flight, librarians, South-South, SouthWest , universities, Nigeria Research Questions Research Question 1: What are the job allocations and designations of librarians who emigrated? Research Question 2: What are the reasons that motivated their emigration from Nigeria? Research Question 3: What is the effect of brain drain of librarians on service delivery in Nigerian universities? Research Question 4: In what ways can brain drain among librarians be reversed? Literature Review Most countries in the West African subregion, nay, the whole of Africa have experienced, at one time or the other, an exodus of highly skilled experts from almost all known