The main purpose of the research was to evaluate the groundwater quality in wet and dry seasons of the study area and determine the areas with high water quality. First, diagrams commonly used in groundwater quality assessment were prepared. Water quality index (WQI) values were calculated by using water quality parameters, spatial distribution maps of WQI and water quality parameters were created by using Geographical Information System (GIS). Groundwater quality mapping was performed with the help of GIS-based analytic hierarchy process. The obtained findings showed that, 91.66% and 77.07% of groundwater samples respectively received at wet and dry seasons have been suitable for drinking. Groundwater quality of around Sivas city center has been rated with 'excellent' water quality. The most important factors affecting the water quality of the research area were the lithological characteristics of the area and agricultural uses. TDS, NO3, SO4, Cr and As are the parameters that negatively affect water quality.