The main goal of this study is to assess the organic geochemical properties and hydrocarbon generation potential of the Tertiary units in the Sivas Basin which is one of the largest sedimentary basins in the Central Anatolia, Turkey. In this investigation, 200 representative samples were collected from the Tertiary sedimentary rock outcrops. In addition, 15 scaled columnar sections were measured and 187 samples were also collected from these sections. Hydrocarbon generating potential and the maturity levels of the Tertiary units along with the geological history in this basin were determined by means of the total organic carbon (TOC) analysis, Rock-Eval pyrolysis, vitrinite reflectance (R-o) and the organic petrographical observations. Kerogen slides of 96 samples containing high TOCs were prepared to determine the organic matter types. Information about maturity degrees were also obtained using the spore fluorescence colours and the vitrinite reflection (R-o).