In this paper, we describe a closed-loop pathological tremor attenuation system using Func- tional Electrical Stimulation (FES). The proposed strategy, which is based on the modulation of joint impedance using FES, was developed after experi- mental evidence was obtained on open-loop trials with tremor patients. The method relies rstly on an online tremor estimation algorithm, which also lters the voluntary motion performed by the patient. Based on this information, the impedance of the trembling joint may be increased accordingly by applying the appropriate stimulation parameters on a pair of antag- onist muscles that act on the joint, thus attenuating the e ects of tremor. An experimental evaluation of the system, which involved 4 healthy subjects and 1 tremor patient, is also presented.