Groundwater is the main resource used to meet the people's drinking water and irrigation needs of the Ain Oussera plain, because of the lack of surface-water resources. This paper intended to evaluate the suitability of groundwater for agriculture and drinking in the Ain Oussera plains. The data of the study were gathered and analyzed from twenty (20) groundwater samples collected to assess the plain groundwater quality, using the Water Quality Index (WQI) and GIS, carried out on physico-chemical parameters, including potential of hydrogen (pH), total dissolved solids (TDS) electrical conductivity (EC), potassium (K+), sodium (Na+), magnesium (Mg2+), and calcium (Ca2+) and major anions (Cl, HCO3, NO3, SO4), as well as, the water suitability test for agricultural purposes, using the sodium adsorption ratio. These parameters were inserted into the GIS platform to create a spatial distribution map for each parameter using the inverse interpolation technique (IDW). The results indicated that the concentrations are within the Algerian permissible limits. The water quality index (WQI), which evaluates the suitability of water for consumption, varies from 31 to 173 with an average value of 81. 70% of the samples from the Ain Oussera plain fall within the excellent and good quality categories. Its water is suitable for consumption (WQI < 100), while 30% is in the poor water category. From the calculation of SAR values, it was found that 90% of the groundwater samples are considered excellent and suitable for irrigation. According to the classification of the United States Salinity Laboratory USSL, the Ain Oussera water quality is classified as poor for irrigation purposes.