When volcanic ash is suffiently fine, that it can pass through a filter and be deposited on a printed circuit board, electrochemical migration (ECM) is expected to be strongly affected by the deposited volcanic ash. In this study, to better understand the influence of volcanic ash on ECM, a water drop (WD) test is performed on two biased Cu electrodes using distilled water droplets containing five samples of volcanic ash from eruptions of different volcanos. From the results, it is seen that all of the volcanic ash droplets exhibited electrical conductivity. The ECM process was accelerated by three of the volcanic ash samples and was negligibly affected by the other two. In addition, both the acceleration and deceleration of the ECM were strongly affected by the content of volcanic ash from Mt. Shinmoe. The WD tests, performed using a commercial SiO2 powder, revealed that the growth of Cu dendrite is physically interrupted by the particles of volcanic ash. Furthermore, the WD tests, performed using the supernatant liquids of each volcanic ash and H2SO4 solutions, revealed electrical conductivity, and that the acceleration of ECM results from water-soluble components, primarily the SO42− ions dissolved from the volcanic ash. Consequently, the acceleration or deceleration of ECM is determined by the balance between the acceleration by water-soluble components and interruption by the particles.