The study examined the roles played by librarians in promoting the use of Open Educational Resources (OER) in their institutions in South-South and South-West geo-political zone of Nigeria. The descriptive survey design was adopted for the study. Data were collected using an online questionnaire and a total enumeration sampling technique was used. Data were analyzed with frequency counts and simple percentages, and Statistical Product and Service Solutions (SPSS) version 23 was used to generate the mean and standard deviation. A total of 200 librarians in university libraries were sent the online questionnaire and 83 librarians responded by filling out the questionnaire giving a total response rate of 42%. The 83 librarians who responded to the online questionnaire was used as the sample of the study. The questionnaire were validated by two experts in research methodology and educational technology. Cronbach Alpha was used to establish the reliability of the instrument, which yielded 0.86. The findings revealed that the librarians have a high level of awareness of the concept of OER and that the majority of librarians were actively involved in promoting the use of OER in their various institutions. Lastly, the study established that inconsistent power supply, lack of library sensitization on the use of OER, poor Internet connectivity, and lack of institutional support for the creation and use of OER were some of the significant challenges to the effective use of OER in universities in Nigeria. Based on the findings, the researchers recommended that academic libraries in Nigeria must meet global standards by promoting universal access to education through the use of OER among others.