Water is the most abundant and wonderful natural resource especially, the fresh water becomes a precious commodity. Today its quality is threatened by numerous source of pollution. The current study deals with the water quality variations influence the phytoplankton diversity in the selected pond of the study area. Several water quality parameters were analysed during the period from January – December 2018 from sampling station sited from Nazareth Puthukulam pond. The water quality parameters like water turbidity, Temperature, pH, Dissolved oxygen, Electrical conductivity, Total Dissolved solids, Hardness, Alkalinity, Calcium, magnesium, sodium, potassium, Chloride, Sulphate, Phosphate and Nitrate were analysed. 37 species of phytoplankton were observed during the study period of which 10 species from the class cyanophyceae, 9 species from the class Chlorophyceae, 9 species from the class Bacillariophyceae, 6 species from the class Euglenophyceae, and 3 species from the class Dinophyceae. The maximum number of species of the class Cyanophyceae were observed during study period. The water quality parameters such as temperature, Alkalinity, phosphate and Nitrates are favourable for the growth of phytoplankton. Correlation study shows positive and Negative correlation with water quality parameters with Phytoplankton.