Electronic absorption and fluorescence spectra of 8-azaguanine in aqueous solution have been studied. Relative intensities of the two peaks observed in absorption are found to change with time. This result can be interpreted in terms of the double-well potential surfaces of the molecule as has been done earlier for guanine. Like guanine, 8-azaguanine also forms a complex with oxygen dissolved in the solution on irradiation in the absorption region and this makes the¹∑_g⁺-³∑_g^- transition of oxygen in the complex allowed by dipole selection rule. The peak of 8-azaguanine fluorescence when excited by radiations of different wavelengths upto 305 nm lies near 400 nm. This fluorescence differs appreciably from that of guanine and can be interpreted as mainly arising from the second triplet excited state of the molecule which may be populated by intersystem crossing from the first singlet excited state.