Two new Ru(II) complexes, Ru(bpy)2L3+ (1 and 2), containing guanidinium ligands have been synthesized and characterized. Both complexes show good selectivity for h-telo G-quadruplex DNA compared to promoters and duplex DNA. Display omitted Two new Ru(II) complexes containing guanidinium groups have been synthesized, characterized and analyzed according to their interactions with different G-quadruplexes and duplex DNA. A FRET assay and a competitive FRET assay showed that both complexes promote the formation and stabilization of the human telomeric (h-telo) G-quadruplex and exhibit higher selectivity compared to promoters (such as c-myc, c-kit and bcl2) or duplex DNA. After binding to G-quadruplex, the two complexes have shown different DNA affinity and fluorescence enhancement. CD analyses further indicate that the two complexes display the ability to induce and stabilize the formation of antiparallel G-quadruplex structures in K+, Na+ or ion-free buffers. The binding stoichiometry with h-telo was of the order of three ruthenium complexes per quadruplex.