The influence of BrCl on the impedance response of both the lithium anode and the carbon cathode in Li/SOCl2 cells was studied. The impedance of the lithium anode increases with storage time while the addition of BrCl to Li/SOCl2 cells decreases the impedance. However, the porous carbon cathode shows a small film resistance before discharge. The addition of BrCl to Li/SOCl2 cells also decreases the impedance, especially for that part of the interface reaction resistance R-2. As a rule, the film resistance of the lithium anode decreases sharply during the early period of discharge, while that of the porous carbon cathode rises rapidly. It follows that the porous carbon cathode is the rate controlling electrode during discharge.