Objective: With constant growth of open science and access to information, access to grey literature also increases. Little is known about grey literature and its use in Slovenia. The purpose of the study is to investigate the use and prevalence of grey literature in Slovenian university libraries. Methods: A survey will be conducted in Slovenian university libraries using an online questionnaire. The questionnaire will be designed to investigate knowing of grey literature among librarians and to identify the categories of grey literature stocked by libraries, the method of acquisition and organization and infuence of open science on accessing grey materials. Anticipated results of the research: The results will show that the use of grey literature is increasing with open science. The survey will also illustrate the different types of grey literature that are being used and it will show also the knowledge of Slovenian librarians about grey literature.