This study was carried out in the Middle Governorate of Gaza Strip, Palestine. The coastal aquifer is the main source of water for domestic, agricultural, and industrial purposes in the study area. During the last three decades the aquifer has deteriorated to a high degree in the quality and quantity due to the over-pumping and the encroachment of seawater. Hydrogeochemical analysis for groundwater samples from 21 domestic wells were done in 2015. The major cations and anions (Na+, K+, Ca2+, Mg2+, Cl-, SO42-, NO3-, and HCO3-) that influence the water quality were determined. The results of analysis show that the groundwater was chemical highly enriched with Na+ and Cl- an indication of seawater intrusion into the aquifer, while K+ and SO42- sourced from fertilizers and wastewater. The regression analysis show significant positive correlation (more than +0.80) between the hydrochemical parameters Na+, K+, Ca2+, Mg2+, Cl-, and SO42. Due to main cations and anions five water types were distinguished in studied wells: (1) Na-Mg-Cl, (2) Na-Cl, (3) Na-Mg-Cl-SO4, (4) Na-Cl-SO4, and (5) Na-Ca-Cl. They represent around 48%, 19%, 19%, 10% and 5% respectively of the total wells. The calcite and dolomite were assessed in terms of the saturation index, where they show mainly negative values indicating under-saturation. The hydrogeochemical behavior is rather complicated and is affected by both anthropogenic and natural parameters.