Four imidazole Cobalt(III) complexes of the type [ Co(en) 2 (L) 2 ] 3+ (en = ethane 1, 2, diamine, L = imidazole) (1), [Co(en) 2 (L) 2 ] 3+ (L = methylimidazole) (2), [Co(en) 2 (L) 2 ] 3+ (L = 1, 2, dimethylimidazole) (3), [Co(en) 2 (L) 2 ] 3+ (L = ethylimidazole) (4) have been isolated and characterized by Elemental analysis, IR, and 1 H, 13 C NMR spectral methods. The binding of the complexes with calf thymus DNA has been investigate d by absorption, emission spectroscopy, viscosity measurements, DNA melting, and DNA photoc leavage. The spectroscopic studies together with viscosity measurements and DNA meltin g studies support that all the complexes bind to CT DNA(=calf thymus DNA) by groove mode. Co mplexes 3 & 4 bind more avidly to CT DNA than 2 & 1. Noticeably, these complexes were fo und to promote cleavage of plasmid DNA pBR322 with incubation of complexes