This study investigated knowledge and utilization of digital applications for effective service delivery in academic libraries in South-South universities, Nigeria. 3 research questions and 3 hypotheses were raised. The population included 181 selected Librarians in the twelve (12) selected universities in South-South, Nigeria as a case study. A sample size of 119 Librarians representing 66% of the population served as respondents. Convenience sampling technique was used for the study. A 25-item questionnaire was used for data collection. Cronbach alpha statistics was used to obtain 0.73 reliability. Mean/standard deviation were used for research questions and z-test statistics was used to test the hypotheses at 0.05 level of significance. The result amongst others revealed that, Librarian in both federal and state universities are knowledgeable about Library Catalogue Apps, Library Card and Account Management Apps, Digital Preservation and Archives Apps and others. Meanwhile, Librarians in both federal and state universities poorly utilize Digital Citation Management Apps, Digital Library Card and Account Management Apps and Digital Preservation and Archives Apps. The analysis also shows that, Librarians do not utilize Digital Augmented and Virtual Reality Apps, Digital Library Events and Notifications Apps, Reading and E-Book Apps, Digital Study and Collaboration Apps and Quick Response (QR) Codes scanners. The challenges academic libraries face in promoting digital applications are inadequate skilled staff to operate digital libraries, difficulty in the enforcement of intellectual property rights, non-utilization of digital library Apps.