The purpose of the study was to determine the epistemological and ontological beliefs of secondary school students concerning some demographic variables such as gender, class, education status of the mother, education status of the father, and the location where science activities are carried out (classroom/laboratory). The participants of the study were composed of 519 female and 510 male students at the 6th, 7th and 8th grades in five different public secondary schools in Istanbul, Turkey. In the study, which was conducted in 2014-2015 school year and reported in 2017, the relational screening model was utilized. The data collection tools comprised Epistemological Opinion Scale and Ontological Opinion Scale developed by Ünal-Çoban and Ergin (2008; 2010). The data were analysed via SPSS 21.0 statistical program. As a result of the data analysis, it was found that the epistemological and ontological beliefs of students were at moderate level and effective in some variables.