Mutilation of library materials is a global phenomenon that must be properly checked to prolong the span of the library materials. This study examined undergraduates’ perception of the influence of book mutilation and defacing on library use in the Federal University, Oye-Ekiti (FUOYE) Library. This study employed the descriptive survey design. The study population comprised all registered undergraduates’ library users at the FUOYE Library who were willing to participate in the study. In all, three hundred and thirty eight (338) students participated in the study. The main instrument for data collection was a structured questionnaire, which was subjected to validity and reliability tests. The data collected for the study were analysed using the relative importance index (RII), while simple regression analysis was used to test the formulated hypothesis. Findings from the study indicated a strong relationship (AdjustedR2= 0.309, F= 150.1, p<.05) between book mutilation, defacing and library use among undergraduates in the Federal University Library, Oye-Ekiti. The findings further revealed that the undergraduates have a high-level of perception on the influence of book mutilation and defacing. The study concluded that more still need to be done in the areas of security of the library materials to forestall the ugly trend of theft, mutilation and defacing in the university Library.