In the present study, the interactions of three different lithium species Li+, Li3+ and CH3Li with several different sites of the most stable tautomers of DNA nucleo-bases are presented. This investigation is based on the results of thermochemical properties, Quantum Theory of Atoms in Molecules (QTAIM) and Natural Bond Orbital (NBO) analysis, obtained at B3LYP/6-311++G(d,p) level of theory. The calculated results showed that guanine and cytosine have more tendencies for interaction with lithium in all above three lithium species. Also, it was shown that for each tautomer of the same nucleobase, coordination mode of lithium highly affects the value of Metal Ion Affinity (MIA). Bidentate base has more lithium affinity and the carbonyl oxygen is generally preferred over amino nitrogen. Furthermore, the analysis revealed the electrostatic nature of interactions. Li+-DNA-Base has the most MIA value and CH3Li-DNA-Base has the least one.