^a Laboratory of Environmental Chemistry, Yantai Institute of Coastal Zone Research for Sustainable Development, Chinese Academy of Sciences, Yantai, Shandong 264003, China 
^b Institute of Oceanology, Chinese Academy of Sciences, Qingdao, Shandong 266071, China
 ^c Graduate University of Chinese Academy of Sciences, Beijing 100049, China 
^d School of Oceanology, Yantai University, Yantai, Shandong 264005, China

A bismuth/multi-walled carbon nanotube (Bi/MWNT) composite modified electrode for determination of cobalt by differential pulse adsorptive cathodic stripping voltammetry is described. The electrode is fabricated by potentiostatic pre-plating bismuth film on an MWNT modified glassy carbon (GC) electrode. The Bi/MWNT composite modified electrode exhibits enhanced sensitivity for cobalt detection as compared with the bare GC, MWNT modified and bismuth film electrodes. Numerous key experimental parameters have been examined for optimum analytical performance of the proposed electrode. With an adsorptive accumulation of the Co(II)-dimethylglyoxime complex at －0.8 V for 200 s, the reduction peak current is proportional to the concentration of cobalt in the range of 4.0×10－10—1.0×10－7 mol/L with a lower detection limit of 8.1×10－11 mol/L. The proposed method has been applied successfully to cobalt determination in seawater and lake water samples.