Abstract: 9 celestite occurences which arefound in Tertiary sediments of Sivas-Ulaş basin, are examined in this study. These celestites are divided in 3 groups according to the relationship between bedding types and the host rock. These groups are: 1. Celestite foundin carbonaceous units (void Jilling-zebroide), 2. Celestite found in detritial units (nodular). 3. Celestite Johnd in evaporitic units(massive) These occurrences are also divided in 3 main petrographic types according to their crystallization and microtextoral characteristics. These types are; a elongated-prismatic, b.tabular and c. fibrous-radial crystals.All these celestite types take place in diffrent levels of the Tertiary evaporitic section. According to the fluid inclusion studiescarried on these occurrences, the homogenization temperatures of voidfilling-zebroide celestites (type I) in Middle-Upper Eocene, concentrate between 320-360 C. nodular celestites (type 2) in Oligocene, between 260-290 C and massive celestites (types 3) in Middle Miocene between 220-270 C. The salinities ofthese types do not differfrom one to another and are about 14-23 % NaCI equivalent. These high salinity and temperature values support the idea ofhydrothermal effects during the formation of Tertiary celestite mineralizations at Sivas basin.