The short-circuit phenomenon caused by dissolution of the NiO cathode in the molten carbonate fuel cell was experimentally investigated. Monitoring CO2 concentration in the anode exhaust gas can be an effective way to detect cell short circuit. The effects of matrix thickness and cathode CO2 partial pressure on shorting were elucidated. The time-to-initial-short-circuit (shorting time) is approximately proportional to the second power of the matrix thickness and the reciprocal of the cathode CO2 partial pressure. This can be explained by the relationship between conductance of the short circuit and the Ni content : of the matrix. A simple model to correlate the conductance with the shorting time was developed. It is concluded that part of the deposited Ni exists as lithiated NiO.