This paper presents the work on the development of a self-breathing mini fuel cell stack. The diameter of the five-cell stack is same as that of a D-size battery, but the length is half of it. The maximum power could reach when operating at . The stabilized operating temperature was at after of operation. The cylindrical structure design makes the cathode more accessible to the ambient air and easier for the heat to be dissipated away. To assemble the fuel cell, only a single bolt was mounted through the centerline of the fuel cell, which reduced the overall weight of the stack. A mathematical 3D model based on the finite element method was developed for the cylindrical structure. The validation of the model was carried out by comparing the measured bulk performance with the predicted performance of the mini fuel cell. The current distribution was calculated and the improved design was suggested.