This study describes a method to prevent electrochemical migration (ECM) using additives, polyethylene glycol (PEG) and imidazole, at different chloride ion concentrations by the water drop test and electrochemical test. The addition of PEG increased the ECM time at high chloride ion concentration, while imidazole increased the ECM time at both low and high concentrations of chloride ions. Also, the rates of dendrite formation and growth varied depending on both the additive and chloride ion concentration, which could be ascribed to the different inhibition mechanisms; the PEG inhibited the initial formation of dendrites by the ether-group, whereas imidazole inhibited both initial formation and the growth of dendrites by heterocyclic organic compound. The surface analysis indicated that the dendrite structures in all solutions consisted of a mixture of trunk and lace types, and the PEG and imidazole did not affect the composition of dendrite.