A series of silver(II) complexes of 5RS,12SR-1,5,8,12-tetramethyl-1,4,8,11-tetraazacyclotetradecane (L) have been synthesized and characterized by X-ray crystallographic analysis and UV–vis absorption spectra. The crystal structure of [AgL(ClO4)2] (1), [AgL(NO3)2]·CH3OH (2), [AgL(H2O)2]Cl2 (3), and [AgL(H2O)2]Br2 (4) showed the macrocyclic ligand L to be in the stable trans-III structure with C-methyl groups at equatorial positions. To our knowledge, this is the first report on the single crystal X-ray structural analysis of halides of silver(II) complex. Usually, silver ions form insoluble inorganic halides, but the stabilization of divalent silver ion by L, enabled characterization of the complex both in the solutions and in crystals. UV–vis analysis revealed that all complexes were in the form of [AgL(H2O)2]2+ in aqueous solution. These complexes in aqueous solution were found to decompose gradually and lose orange color. The decomposition rate constants of these complexes were evaluated as 0.1012, 0.0971, 0.0981, and 0.2104 h−1 for complexes 1–4, respectively. The decomposition was accelerated by Br− and I− anions.