The paper presents a PMU prototype specifically developed for active distribution network applications. The paper describes the method developed to accurately measure the synchrophasors, its implementation into a real-time microcontroller and the relevant characterization in both steady state and transient conditions. Concerning these last points, the paper presents a test procedure suitably conceived to characterize the PMU with both steady state – single tone and distorted – and frequency-varying signals simulating power systems electromechanical transients. The results show that the developed PMU exhibits high accuracy levels that are not modified by the harmonic distortion of the reference signal and by its frequency-varying transient behavior and compatible with their use into power distribution networks.