Abstarct: Hydrocarbon Contaminants are one of the main cause at groundwater contaminaiton. Fajr Gas Refinery, the largest one in IRAN, locates in the Riz plain at Bushehr Province. Due to the high volume of industrial wastwaters, storage reservoirs and transpontation of the oil products, as well as recently spills of the effluents to the adjecent river, probable contamination at the Riz aquifer has been increased. Therefore, the aim of this study is to investigate the effects of Fajr gas refinery on the Riz aquifer. In this regard Sampling from effluent, surface water and ground water was carried out in dry season (June, 2016). The parameters including EC, TDS, pH, main ions, selected heavy mextals, organic matter (TOC) and hydrocarbons (TPH, PAHs and BTEX) were measured. The results showed EC, pH and the major ions of the effluent are lower than the surface water, but concentration of heavy mextals are much higher than that of the surface water. High contamination with iron, zinc and lead. Is observed in effluent. TOC and TPH levels in wastewater and surface water samples are much higher than the EPA standard. Among BTEX compounds, benzene concentration in wastewater samples is 1634 μg / l, which is higher than both WHO and EPA standards. Concentrations in the all wastewater samples in which PAHs have been identified are higher than the standard values. Spatial variations of EC, pH, sulfate and calcium in ground water indicate a decrease in concentration by increasing the distance from the refinery. The highest level of aquifer contamination with heavy mextals is related to Zn. The results of TOC and TPH in groundwater are consistent and indicate the aquifer contamination with organic matter and the aquifer oil pollution is in the moderate level. The aquifer of the study area is only contaminated with benzene in some samples. BTEX spatial variations indicate enhanced concentrations at the points closer to the refinery and upstream of Shahre khas village, due to the decrease in surface runoff velocity and so increase of infiltration rates. Amon the 16 measured PAHs 9 constituents were detected in groundwater and the highest concentration is pyrene. Totally, the quality assessment of water resources indicates the impact of Fajr gas refinery on contamination of surface water resources and the Riz aquifer.