The study investigates utilization of the library and its effect on academic achievement of undergraduates in selected university libraries in South-South, Nigeria. A descriptive survey method was adopted for the study. Three research questions were formulated to guide the study. The population of the study consists of 300 undergraduates from the university under study. A total of 300 copies of questionnaire were distributed and 243 copies of the questionnaire were retrieved using descriptive statistics mean and percentage mean score of 2.5 and above and percentage score of 50% were considered as acceptable. The study revealed that learning, research, preparation for exams are the benefit of utilizing the university libraries. Factors impeding the utilization of the library includes, obsoletes books, poor infrastructure, lack of proper orientation to library usage and as well as erratic power supply. Strategies to improve on utilization of the library to aid academic achievement are provision of current books; infrastructures, constant power supply as well as library orientation to undergraduates.