Abstract The abuse of library materials defined in terms of theft, mutilation, unauthorized borrowing and vandalism was investigated in University of Port Harcourt (Uniport) in Nigeria and King Fahd University of Petroleum and Minerals (KFUPM) in Saudi Arabia. The study sought to find out the ways the collections of the two institutions were abused by various classes of readers and for various reasons. By interviewing librarians, and analysis of collection use records, it was revealed that students, as well as faculty, staff and external readers indulged in abuse of library materials, motivated by situational, conceptual, attitudinal and other factors. It was observed, however, that Uniport had more problems with the misuse of library materials than KFUPM. Recommendations relating to library building design, tightening of security, generous and flexible loans policies, etc., were made for improved collection protection. Besides, public relations campaign and multilateral co-operation on book theft detection would help to discourage in particular the uninitiated or new converts from any acts of library abuse.