This paper is a study of the origin and diagenetic history of the Upper Jurassic dolomites of the Mozduran Formation, from north eastern Iran, in the Kopet-Dagh Basin. Petrographic and geochemical studies indicate that the Mozduran dolomites were subjected to a complex diagenetic history, resulting five different dolomite—rock textures. Dolomite type 1 consists of very fine to finely crystalline dolomite, forming penecontemporaneously or by early replacement of carbonate mud, soon after deposition, with Mg possibly derived from seawater. Dolomite type 1 has the most enriched δ180 values (−1.1‰ PDB), compared to other dolomite types. On the basis of crystal size, fabric, and absence of fossils, dolomite type 1 is considered to have been formed in a supratidal to upper intertidal setting, under near surface, low temperature (~34°C) conditions. Dolomite type 2 consists mainly of euhedral rhombs floating in a limestone matrix. This dolomite type resulted from replacement of precursor calcium carbonate, mainly during early shallow burial, and Mg was probably derived from dissolution of high-Mg calcite. Dolomite type 3 is considered to represent a diagenetic replacement of pre-existing limestone and/or recrystallization of an early formed dolomite, possibly after some burial. Dolomite type 4 has medium to coarse nonplanar crystals, often characterized by nonmimically replaced allochems, developed during deep burial (~3.5 to ~4 km), in temperatures ranging from 84 to 113°C. The last dolomitizing events are represented by dolomite type 5, which consists of coarsely crystalline planar-C (cement) dolomite, lining voids, vugs and fractures. This dolomite type has been interpreted as having formed at the latest diagenetic stage, at elevated temperature, ranging from 94 to ~110°C. Dolomite types 4 and 5, with de highest temperatures of formation, possibly formed during the period of maximum burial, between Paleocene and Eocene time. Compaction of shales and clay diagenesis, combined with basinal brines, could produce enough magnesium for shallow to deep burial dolomitization (dolomite types 3 and 4), and dolomite cementation (dolomite type 5). The presence of higher concentrations of organic carbon in dolomites than limestones (~2 to 5 times higher), may indicate that dolomitization occurred preferentially in limestones that originally had higher concentrations of organic matter.