The NH-tautomerization in the lowest singlet S1 state of the 5,10-mesityl-15-(2,6-dichloropyrimidinyl)-corrole free base was studied in temperature range 278—318 K. It was shown that the NH-tautomerization was the dominant channel for the deactivation of the electronic excitation energy of the short wavelength T2 tautomer. The NH-tautomerization was found to cause the significant changes in quantum yields of the electronic energy deactivation of this tautomer as a function of temperature. When temperature rises up to 318 K, almost 90% of the electronic excitation energy of the corrole ensemble in the solution accumulates on the singlet S1 state of the long wavelength T1 tautomer after phototautomerization.