The present studies were carried out on the diversity of phytoplankton in relation to physico- chemical parameter from July 2012 to June 2013 in chikkakere, Periyapatna, Mysore, Karnataka. The water samples were analyzed to physical and chemical parameters by following the standard methods of APHA (2005) and Trivedi and Goel (1984). The quantitative analysis of phytoplankton was done by Lackey’s drop method modified by saxena (1987). Total 29 species were recorded which are belonging to Bacillariophyceae, Chlorophyceae, Cyanophyceae, Euglenophyceae and Desmidiaceae. Diversity indices have been discussed by using PASTA Software Program. The diversity indices includes Shannon and Weiner index, Berger and Parker index, Simpson index, Margalef’s index and Pielous index which determines status of the water body. The statistical program Pearson’s correlation matrix has been discussed by using SPSS 20.0 Software program. The Pearson’s correlation matrix explained Total Hardness is directly correlated with calcium, chloride and total alkalinity. The higher values of nitrate and phosphate observed in the month of May which leads in formation blooms in the lake. Microcystis aeruginosa blooms are dominant and occurred throughout year in the lake.