The relative energies and tautomeric equilibrium constants of Cyanuric acid (1,3,5-triazine-2,4,6-triol) have been calculated at DFT/B3LYP level of theory using 6-311++ G (d,p) basis set in gas phase and different solvents by using PCM model. The results indicate that the keto tautomer (CA1) is the most stable in the gas phase and other solvents. The order of stability of isomers was found to be CA1 > CA3 > CA2 > CA6 > CA11 > CA10 > CA7 > CA4 > CA5 > CA9 > CA8.The calculated tautomeric equilibrium constants with respect to the most stable tautomer CA1 in both gas phase and in different solvents. The mean polarizabilities were calculated and the order was Gas > THF > ethanol > DMF > water.