Abstract: Groundwater quality is an inevitable factor for sustainable agriculture as a source of irrigation water. Therefore, the study was conducted in an irrigated sand dune area of northwest Honshu island in Japan to evaluate the groundwater quality for irrigation. Three observation wells were installed in the investigated field made of Poly Vinyl Chloride (PVC) pipe with three plastic tubes to collect groundwater of 2.0, 2.5 and 3.0 m. The sampling was performed every month from January to November, 2005. Assessment of groundwater quality was performed on the basis of Total Dissolved Solids (TDS), concentration of sodium (Na), calcium (Ca) and magnesium (Mg), Sodium Absorption Ratio (SAR), total hardness (HT) and concentration of phosphate phosphorus (PO4-P). Total dissolved solids in groundwater was ranged between 145.5-249.4 mg L-1 during the investigation period, revealed that irrigation using groundwater of the study area would not cause salinity hazards. Cocentrations of Na, Ca and Mg were decreased with depth throughout the investigation period. The average concentration of Na and SAR value were 18.8 mg L-1 and 0.81, respectively. Since groundwater of the study area contained low concentration of Na with low SAR values, there would not be any possibility of sodium hazards from irrigation using groundwater. On average groundwater of the study area contained 27.5 mg L-1 Ca and 9.35 mg L-1 Mg, which might contribute to moderate hardness of groundwater in the study area.