A study was carried out to assess the nitrate and fluoride contamination and hydrogeochemical characterization of groundwater in south-west region of Delhi State during the year 2007-08. The study area was selected as Najafgarh Sub Division of South West District of Delhi State, India. The groundwater samples were collected from the same tube wells of randomly selected 20 villages in Najafgarh Sub Division during both pre and post-monsoon seasons (May and October, 2007). Results indicated that quality of groundwater samples in terms of total soluble salts (ECiw) was in the range of 1.28-11.40 and 1.16-8.19dS m-1 in pre and post monsoon seasons, respectively. Based on the relative dominance of different cations and anions, the groundwater was classified as Na-Mg-Ca and Cl-HCO3-SO4 type. Nitrate-nitrogen in groundwater samples during pre and post-monsoon season ranged from 2.50 to 45.20 mg L-1 and 2.30 to 42.40 mg L-1 with mean value of 9.24 and 8.90 mg L-1 and fluoride concentration ranged from 0.14 to 3.28 mg L-1 and 0.12 to 3.25 mg L-1 with mean values of 1.21 and 1.20 mg L-1, respectively. Nitrate- nitrogen concentration of groundwater was found higher than permissible limit (10 mg L-1) in the villages of Mitraon, Ghumanheda, Dhansa, Hasanpur and Daulatpur of Najafgarh Sub Division. Fluoride concentration more than permissible limit (1.5 mg L-1) was observed in Surheda, Kharkhari Round, Ghumanheda, Daryapur, Chhawala and Uzwa villages of the Najafgarh block. The higher concentrations of salinity, sodicity, nitrate and fluoride in groundwater having adverse effect on plant growth and also causes the serious health problems to human beings. The higher concentrations of salinity and sodicity reduces the yield of the crops and the concentration of nitrate-N more than 10 mg L-1 and fluoride more than 1.5 mg L-1 in groundwater causes the Methemoglobinemia or Blue Baby Syndrome and Fluorosis diseases in human as well as in animals, respectively.