Dissolved calcium distribution in the Cochin Backwater was studied in December 1973 at forty station. The ratio of calcium to chlorinity value in the estuary was found to deviate discontinously as compared to sea water. The ratio of calcium to chlorinity ranged from 0.02122 to 0.02246 and 0.0714 for different samples. In a majority of the samples, higher values of calcium relative to chlornity were found with decreasing chlorinity. The distribution of calcium-chlorinity ratio of the estuarine waters at different stations showed 5 to 15 % increase over at the adjacent sea water.