<p>In this study, we have demonstrated electrochemical synthesis of polyphenylene (PP) deriving from 1,4-bis(trimethylsilyl)benzene using a flow microreactor. The electrochemical flow microreactor allowed effective synthesis of a soluble PP without its deposition. The molecular weight of PP could be controlled by selecting reaction conditions for the electrochemical polymerization in the microreactor. In addition, the role of trimethylsilyl (TMS) group in this reaction process was clarified by the comparison to the polymerization of unsubstituted benzene.</p>