A new solid state fluoride ion selective electrode composed of 70% Ag(2)S, 10% Cu(2)S and 20% CaF(2) has been developed. An analytically useful potential change occurred, from 1x10(-6) to 1x10(-1)M fluoride ion. The slope of the linear portion (1x10(-1)-1x10(-5)M) was about 26+/-2mV/10-fold concentration changes in fluoride. It was found that pH change between 1 and 8 had no effect on the potential of the electrode. There was no interference of most common cations such as K(+,) Na(+), Ca(2+) and Mg(2+) and anions such as Cl(-), NO(3)(-), SO(4)(2-) and PO(4)(3-). The lifetime of the electrode was more than 2 years, when used at least 4-5 times a day, and the response time was about 60s. The measurements were made at constant ionic strength (0.1M NaNO(3)) and at room temperature. This electrode has been used for the determination of fluoride ion in Ankara city tap water and in bottled spring water using standard addition method. The validation of the electrode has been made with a commercial fluoride ion selective electrode (Orion) and high consistency was obtained.