This work examined the nature of delinquency among library staff and users in academic libraries. To this end, the study focused on the extent of delinquency in academic libraries, the most serious delinquent acts, causes of delinquency, the characteristics, and attitude towards the library of users who admitted involvement, methods and opportune time for stealing and mutilation, the extent of library staff involvement and the various measures in place to detect and deter delinquency. Survey research method was used. The population of the study is made up of five selected academic libraries in Edo and Delta states. The total sample for the study was 722 library staff and student drawn through systematic random sampling technique. Questionnaire was major tool for data collection. Percentages, means, standard deviation and summation of weighted values have been employed to analyse data in this work. The study revealed that delinquency is a serious problem confronting academic libraries; withholding and mutilation are the most serious delinquent acts.