ABSTRACT: Geothermometers are one ofthe most important methods used for determining the geothermal water reservoir temperature. Chemical content ofthe thermal water that was acquired by the water-rock interaction is used in the geothermometer equations. Determination of possible reservoir temperature ofthe thermal water is quite important for development and operation of the thermal waters. in spite ofbeing lots of geothermometer type like cation, silica, gas and isotope, generally cation and silica geothermometers arepreferred because their analyses and evaluations are easy. in the scope ofthis study, a computer programme has been prepared by using ofthe Microsoft Visual Basic 6.0 programming language and aim of this programme is determining the thermal water reservoir temperature by silica and cation geothermometer equations. Majör ion order which denotes the water type; majör ion balance which indicates the accuracy ofthe water analyses; and maturity index which indicates the application ofthe Na-K geothermometers are suitable or not to thermal water are determined by this programme in addition to the geothermometer calculations. Appropriateness of the reservoir rock mineral composition to the based mineral used in geothermometer equations, the chemical equilibrium behveen water and rock, cold water mixing, chemical changes in the thermal water when it was ascending, etc. must always be taken in to consideration during the geothermometer applications, in terms ofevaluations and reliability.