Thirty-one ground samples were collected in the Hidehran and Alburayhi basin, northwest of Taiz city, from Tertiary age aquifers. A hydrogeochemical investigation was conducted in the study area. The fluoride ions along with other chemical parameters were analyzed to determine the hydrochemical characteristics, water types and evaluate the main source of fluoride in groundwater of the aquifer. Fluoride ion concentrations in the groundwater in excess of WHO recommended limit of 1.5 mg/l for drinking water occurs throughout the area. Of the 31 well samples to be contained with fluoride concentration in excess of the recommended limit, the hydrogeochemical concentration of ions in the groundwater. The saturation indices (SI) of fluorite (CaF2) and calcite (CaCo3) in the groundwater samples showed that the majority of the samples are oversaturated with respect to calcite; and undersaturated with respect to fluorite. The population of the study area is at a high risk due to excessive fluoride intake, especially when they are unaware of the amount of fluoride being ingested.