The electronic properties of nanographene and their chemical modification effect are reviewed. The presence of the zigzag edge in nanographene gives edge states, which are the non-bonding spin-polarized π -electronic states between graphene π - and π ^*-bands, and are localized at the zigzag edge sites. The edge states having the large density of states at the Fermi energy play an important role not only in the electronic properties of nanographene but also in view of chemical reactions. The fluorine termination of the edge sites causes the reduction in the spin polarization of the edge state, while bromine termination enhances the spin-orbital coupling of the edge state.