Abstract: There has been an increasing global trend in nitrate contamination of groundwater, and especially in China. This has raised concern for increased nitrate-caused methemoglobinemia and cancer. Available technical data and experience have indicated that denitrification was a more acceptable method for nitrate removal than reverse osmosis and ion exchange. This paper systematically reviewed the denitrifying micro-organisms, denitrification mechanisms, carbon sources, and laboratory/field-scale nitrate removal processes for effective denitrification of groundwater. Key problems with previous studies were also pointed out. As the reviewed showed that there were more related laboratory research than field research, information on the characteristics of specific micro-organisms involved in on-site nitrate removal from groundwater was limited. In addition, the utilization ratio of carbon sources was low and nitrate removal rate from groundwater was also slow. Despite the above issues, metabolic pathways of effective denitrifying micro-organisms used in nitrate removal from groundwater were still unclear. Hence the proposed relevant suggestions included: 1) In situ exploitation of denitrifying micro-organisms. Identification of the specific functions and ecological behaviors of micro-organisms via advanced molecular methods and function gene analyses. 2) Selection of the best sources of carbon and metabolic processes of microorganisms during nitrate removal from groundwater. 3) Clarification of the denitrification processes of nitrogen transformation in groundwater. All the above suggestions provided the basis of the theory of nitrite removal from groundwater, making both the theory and practice more reliable combination.