The filiform corrosion of Mg-3Zn Mg alloy in various corrosion environments was investigated by scanning electron microscopy (SEM) observations, scanning vibrating electrode technique (SVET) and electrochemical measurements. The results indicate that corrosion filaments can cross grain boundaries and fine precipitation phases to develop continually. The propagation of filiform corrosion is greatly associated with the existence of C1(-) in the solutions. A small amount addition of F- or SO42- to the NaCl solution can delay the initiation of filiform corrosion, while abundant F(-)or SO42- addition can change the corrosion forms. The micro-anodes and micro-cathodes transfer dynamically with the growth of corrosion filaments. Mg-3Zn alloy exhibits a filiform corrosion mode at the applied anodic potentials but keeps intact at the applied cathodic potentials. (C) The Author(s) 2017. Published by ECS. This is an open access article distributed under the terms of the Creative Commons Attribution 4.0 License (CC BY, http://creativecommons.org/licenses/by/4.0/), which permits unrestricted reuse of the work in any medium, provided the original work is properly cited. All rights reserved.