Positive perception of the ethical issues in libraries by library personnel in polytechnics could motivate them to adhere to the ethics of library service delivery. However, reports from studies have shown that while some library personnel had a positive perception of some ethical issues, they also had negative perception of other ethical issues. Demographic factors could determine the type of perception that library personnel have towards ethical issues in libraries. Therefore, this study examined demographic factors as determinants of perception of ethical issues in libraries by library personnel in selected polytechnics in Southwestern Nigeria. The study adopted the descriptive survey research design of the correlational type. The population of the study consisted of 169 library personnel of the Polytechnic, Ibadan, Oyo State, Yaba College of Technology, Lagos State and Moshood Abiola Polytechnic, Ogun State. All the library personnel participated in the study and data were collected through the questionnaire. Results showed that out of the demographic factors, age (r=.228**; N=148; p<0.05), marital status (r=.222**; N=148; p<0.05), religion (r=.294**; N=148; p<0.05) and years of experience (r=.257**; N=148; p<0.05) had a positive significant relationship with perception of ethical issues in libraries. Therefore, in planning workshops that will impact positively on the perception of ethical issues by the library personnel, these demographic factors should be put into consideration.