**Abstract**

Fluorosis continues to be an endemic problem in Yemen. More areas are being affected by fluorosis in different parts of this country. The present study aims to identify the intensity and the spatial extent of fluoride concentration in groundwater of the southern part of the upper Wadi Rasyan, Taiz, Yemen. 93 sampling points were selected; the sampling included all types of sources of groundwater and all types of aquifers. The results show that 71% of samples exceed the WHO drinking water guidelines value of 1.5 mg/l, and there are wide variation for groundwater's content of fluoride in the same aquifer (whether, volcanic and alluvial) and in the same of groundwater type, and these variations between the different water types or between the different depths of water (alluvial and volcanic aquifers) are not significantly different. The high concentration of fluoride in groundwater of the volcanic aquifer is likely because of the nature of geology formations by the waterrock interaction result of long-time residence of water in contact with the geology formation. The high concentration of fluoride in the alluvial aquifer likely resulting the waste of urban and industrial activates sources, the over exploration of groundwater, the arid climatic and the activities agriculture.

**Keywords:** fluoride, spatial distribution, GIS, Al-Burayhi and Hedran, Al-Hawban, upper Wadi Rasyan, Taiz and Yemen
