In this paper, three kinds of imidazole derivatives, 2-(4-methylphenyl)-4,5-di(2-furyl) imidazole (MDFI), 2-(4-nitrophenyl)-4,5-di(2-furyl) imidazole (NDFI), and 2-(4-tert-butylphenyl)-4,5-di(2-furyl) imidazole (t-BDFI) were synthesized. In an alkaline medium, the chemiluminescence (CL) reaction of imidazole derivatives with H 2 O 2 has been investigated. It was also found that MDFI/H 2 O 2 and t-BDFI/H 2 O 2 systems gave strong CL. When Co 2+ was added into the two CL systems, the CL intensity was remarkably enhanced. In the optimum conditions, the CL intensity is linearly related to the logarithm of concentration of Co 2+ . The linear ranges are 5×10 −9 –2.5×10 −7 mol/L for MDFI/H 2 O 2 system and 5×10 −9 –2.5×10 −7 mol/L for t-BDFI/H 2 O 2 system, and the corresponding detection limits are 1.2×10 −9 mol/L and 1.1×10 −9 mol/L, respectively. The method was applied to the determination of Co 2+ in vitamin B 12 injection. Furthermore, the CL mechanism was also discussed.