PEDOT:PSS has not conductivity enough to be replaced for indium tin oxide (ITO). Recently lots of secondary dopants such as ethylene glycol and DMSO have been proposed and applied to PEDOT:PSS for the conductivity enhancement. The authors have been studying the effect of organic compounds with hydroxyl groups such as alcohols, glycols and bisphenol compounds on the conductivity of PEDOT:PSS and its conductivity enhancement mechanism. Alcohols such as methanol, ethanol, iso-propanol etc., glycols such as ethylene glycol, diethylene glycol, poly(ethylene glycol) etc., and bisphenols such as 4,4’-dihydroxydiphenylsulfone (BPSO), 4,4’-dihdroxydiphenylsulfide (BPS), 4,4’-dihydroxydiphenylether (BPO), 2,4’-dihydroxydiphenylsulfone (24-BPSO) etc. were studied as a secondary dopant of PEDOT:PSS. The mixture of organic compound and PEDOT:PSS was dissolved in iso-propanol/water mixture. The solution was coated on the glass plate and dried. The surface resistivity (Rs) of the thin films was evaluated. It was found that there was a relationship between Rs values of the dried PEDOT:PSS/alcohol or glycol mixtures and solubility parameter (SP) of alcohols and glycols which support that the conductivity enhancement was possibly ascribed to the removal of PSS from the surface of PEDOT:PSS nanoparticles clusters by the solvent. On the other hand, there was a large difference in the conductivity enhancement effect among the species of bisphenol compounds. The addition of BPSO or 24-BPSO contributed to the conductivity enhancement of PEDOT:PSS, while BPO and BPS showed increase of its ñ value, although there is no difference in SP value among them. It was found that Rs values of dried PEDOT:PSS/bisphenol mixture has no relationship with SP values of bisphenol, but with electron withdrawing ability of substituents on benzene ring of glycols, that is, acidity of OH groups. The action mechanism of secondary dopant BPSO to PEDOT:PSS is now under study.