Two new dendrimers, 4,4',4"-((1E,1E',1E")-(1,3,5-triazine-2,4,6-triyl)tris(oxi))tris(3-methoxibenzene-4,1-diyl))tris(mathaneylidene))tris(azaneylidene))tribenzoic acid (TVTBA) and ((N,N',N"E,N,N',N"E,N,N',N"E)-N,N',N"-((((1,3,5-triazine-2,4,6-triyl)tris(3-methoxibenzene-4,1-diyl))tris(pyridine-2- amine)) (TVTAP), have been synthesized by reaction of cyanuric chloride, vaniline, para- aminobenzoic acid, and ortho -aminopyridine. Four new trinuclear Ru(III) complexes, [Ru 3 Cl 9 (OH 2 ) 3 (TVTBA)], [Ru 3 (DMF) 12 (TVTBA)](TFA) 9 , [Ru 3 Cl 9 (OH 2 ) 3 (TVTAP)], and [Ru 3 (DMF) 12 (TVTAP)](TFA) 9 , have been prepared with the new dendrimers, TVTBA and TVTAP. All dendrimers and their complexes were characterized by elemental analysis, FT-IR, UV-Vis and 1 H-NMR. The optimized structure of TVTBA was obtained using the DFT method by the Gussian 09 software. The B3PW91 and B3LYP basis sets show that the anti structure of TVTBA is more stable than the syn structure. The electrocatalytic activity of [Ru 3 Cl 9 (OH 2 ) 3 (TVTAP)] on the reduction of CO 2 to CO was investigated in DMF by cyclic voltammetry method. The results reveal that the Ru(III)/Ru(II) redox couple observes in the positive potential. TVTAP shows a pseudo-reversible behavior at negative potential. The electrocatalytic activity of complex was also studied in several reaction conditions including catalyst concentration, cell temperature, scan rate, and CO 2 purging time. The results show that the electrocatalyst concentration of 3 mM, and cell temperature of 20 °C are the best reaction conditions to get the maximum electrocatalytic activity for the Ru(III) complex. Keywords: dendrimer, Ruthenium(III) complex, electrocatalytic activity, Carbon dioxide, Carbon monoxide, cyclic voltammetry.