Groundwater　quality　assessment　is　vital　to　protect　this　resource.　Therefore,　the　aims　of　this　study　were　to　evaluate　the　hydro-chemical　quality　of　the　Marvdasht　aquifer　located　in　the　semi-arid　region　of　Iran　and　to　map　the　groundwater　quality　parameters.　For　this　purpose,　a　mean　data　of　11　groundwater　quality　parameters　collected　from　49　wells　(2010-2015)　were　used.　Pie,　Schoeller　and　Piper　diagrams　were　used　to　determine　the　dominant　ions　and　type　of　water.　Ion　ratios　and　Gibbs　diagrams　were　used　to　illustrate　the　chemistry　and　processes　in　the　groundwater.　Spatial　distribution　of　quality　parameters　were　mapped　using　ArcGIS.　Results　showed　that　the　water　type　is　Na-Cl　and　Cl-　with　abundance　orders　of　CL-　＞　SO42-　＞　HCO3-　and　Na+　with　abundance　orders　of　Na+　＞　Mg-2　+　＞Ca2+　＞　K+　are　dominant　anion　and　cation,　respectively.　Gibbs　diagrams　revealed　that　geological　formations　control　the　groundwater　chemistry　in　66%　of　the　groundwater　samples.　Based　on　the　Wilcox　diagram,　only　24%　of　the　samples　fell　into　the　C-4-S-4　class　with　high　salinity　and　alkalinity　hazard.　The　maps　showed　that　generally　groundwater　in　the　north　of　the　study　site　has　better　quality　than　that　the　south　of　the　study　site,　where　the　existence　of　dolomite　and　chalky　formations　leads　to　decreasing　water　quality.