Through the combination of steady state absorption/emission, time resolved absorption spectroscopy, and low-intensity laser irradiation experiments, we have investigated the excited state relaxation pathways for both 5mCyd and Cyd upon excitation at 267 nm and reported a threefold higher relative photostability of 5mCyd compared to the canonical RNA nucleoside Cyd in phosphate buffer pH 7.4. We have also shown that a 1 n* state of Cyd decays with a lifetime of ca. 44 ps in aqueous solution upon excitation at 267 nm and detected no spectroscopic evidence for the population of a nanosecond excited state. The 1 n* state is directly implicated in the formation of 6-hydroxycytidine and other primary photoproducts. The slower S1 * state internal conversion to the ground state observed in 5mCyd compared to Cyd, is proposed to be due to the higher energy barrier required to access the ethylenic C5-C6 twist S1/S0 conical intersection due to the presence of the methyl group. We highlight that even though the 1 * excited state decay is 5-fold slower in 5mCyd than in Cyd, the three-fold decreased photodegradation rate demonstrates that monomeric 5mCyd is more photostable than Cyd in aqueous solution at pH 7.4 and suggests that a 1 n* state plays an important role in the formation of photoproducts in Cyd, as previously proposed. Given that the primary photoproducts observed in 5mCyd have similar absorption spectra than those of Cyd (see Figure in the SI), it is possible that an analogous 1 n* state is also populated in 5mCyd but at ca. three-fold lower yield than in Cyd. This idea, together with the fact that stimulated emission in 5mCyd occurs in the same spectral region, could explain why a