Monthly fluctuations of physico-chemical characteristics were carried out in Uppanar estuary south east coast of Cuddalore District, Tamil Nadu, India, for a period of twelve months (January 2017 to December 2017). Eight various physico-chemical parameters were analyzed by using standard methods (APHA, 1998). Water temperature varied from 23.62 to 31.05°C, pH ranged from 7.62 to 8.42. Turbidity was from 35.75 to 53.02 cm, Dissolved oxygen content varied between 4.24 to 6.23 mg/L, salinity (17.27 to 26.27 ppt), calcium (123.15 to 244.45 mg/L), nitrate (0.40 to 0.59 mg/L) and ammonia (0.04 to 0.17 mg/L) also varied independently.