The Chia Gara Formation (M.Tithonian-Berriasian) from the well K-109 has been studied in detail sedimentologically and from hydrocarbon potentiality point of view. The studied rock samples obtained from the North Oil Company, Kirkuk. The formation consists of alternation of dark fissile calcareous shale and organic-rich limestone layers (argillaceous limestone). The limestone beds are thin and lacking any bioturbation. The lower contact is conformable with the Barsarin Formation and the upper boundary is gradational with the Karimia Formation. The radiolarian mudstone-wackestone is the major microfacies in the succession. Nearly all radiolarians are filled by calcite as a major diagenetic process.The TOC% has a range between 0.62% and 7.26%, with high values in the lower part of the Formation. The type of organic matter is mostly brown amorphous as seen in palynological slides and the TAI is about 3+.The Rock-Eval Pyrolysis results indicate low value of HI and the type of kerogen is type II-S & III. Several diagrams used for determining the type of kerogen,maturity and oil or gas potentiality.The kerogen is mature and in oil zone.The sulfur content as determined from CNS analyzer is high in the lower part of the sequence. All sedimentology and organic geochemistry data reveal that the formation deposited in deep shelf basin (Late Jurassic passive continental margin of the Arabian Plate) with quiet and warm water. The euxinic environment can be concluded from the absence of microboring and high rate organic matter preservation as well as the abundance of pyrite. The Chia Gara sediments could be considered as an important source rock for petroleum in accumulated oil in Kirkuk structure.