This paper studies the effect of electromagnetic damping ratio on the optimum load resistance of an electromagnetic vibration energy harvester. A mathematical model describing the power output of the harvester was derived and analyzed. It was found that for cases where the electromagnetic damping is much lower than the mechanical damping of the harvester, the optimum load resistance value is equal to the coil resistance value. However, if the electromagnetic damping is high, then the optimum load resistance does not equal to coil resistance. In addition, this optimum value is not necessarily obtained when the electromagnetic damping is equal to the mechanical damping. For this case, the optimum value will depend on the mechanical damping ratio, electromagnetic damping ratio, coil resistance and load resistance. A good correlation was observed between the mathematical model and experimental measurements. © 2018 IEEE.