Provided is a polymerization liquid for electropolymerization, which uses a solvent that is mainly composed of water, which is greatly increased in the amount of a monomer contained therein, and which is capable of quickly forming a conductive polymer layer having high conductivity and heat resistance, A polymerization liquid for electropolymerization of the present invention contains: a solvent that is composed of 100-80% by mass of water and 0-20% by mass of an organic solvent; at least one monomer having a pi-conjugated double bond; at least one supporting electrolyte; and at least two nonionic surfactants. The at least two nonionic surfactants are composed of at least one acetylenol surfactant and at least one water-soluble nonionic surfactant other than the acetylenol surfactant. Due to the combination of the two nonionic surfactants, the amount of the monomer emulsified with the solvent can be greatly increased.