An electrorheological (ER) fluid, consisting of polydisperse dedoped polyaniline (PANI) particles, having irregular shapes, dispersed in silicone oil, was subjected to cyclic strain annealing treatments using oscillatory shear, under an external electric field. After each annealing period, the sample was subjected to a controlled-strain sweep, to determine the yield stress, and to erase the ER structure. During each annealing cycle, the storage modulus and the yield stress were observed to increase, and the loss modulus to decrease, each eventually approaching an asymptotic constant value. These observations in oscillatory shear complement our previous observations of a strain-hardening effect in a PANI/silicone oil ER fluid subjected to unidirectional creep tests.