Abstract: "Three-Grille-Mode" septic tank is a common approach used in renovating latrines in the rural areas in Jiangsu,accounting for about 50% of the total sanitary latrines in the area.Its treatment efficiency directly affects quality of the rural water environment.A total of 168 normally running "Three-Grille-Mode" latrines in 9 cities(counties) of Jiangsu were selected as objects of the research.In the period from June to August,2006,water samples were collected at the inlet and outlet of the latrines 3 times consecutively with an interval of 5 days.Analysis of the samples showed that "Three-Grille-Mode" septic tanks could reduce COD_Cr by 48.51%,TN by 6.83% and TP by 23.92%,and the efficiency varied with the influent concentration,and followed a decreasing order of South Jiangsu>Central Jiangsu>North Jiangsu.Generaly its treatment efficiency was lower than the biogas-digester′s.The treated water flowing out of the septic tanks fails to meet the criteria of the national standard for wastewater discharge and its discharge will significantly affect the environment.