Soluble conductive polypyrrole (PPy) with room temperature conductivity (2-18 S/cm) has been synthesized by doping polypyrrole with mixed acid containing camphor sulfonic acid (CSA) and dodecyl benzene sulfonic acid (DBSA). The solubility and the room temperature conductivity of PPy doped with mixed acid were measured as a function of component of CSA-DBSA mixed acid, and the structure of PPy was characterized by Fourier transform infrared (FTIR), ultraviolet-visible (UV-vis) spectra, X-ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM) and thermogravimetric analysis (TGA). PPy doped with DBSA-CSA mixed acid is soluble in m-cresol although PPy doped only by CSA is completely insoluble in any solvent. The solubility of PPy doped with mixed acid increases with an increase in the fraction of DBSA in the mixed acid, while the room temperature conductivity of the PPy increases with increasing CSA molar fraction. The UV-vis spectra and electron spin resonance (ESR) measurements showed that both polaron and bipolaron are the charge carrier in the doped PPy with mixed acid. It was proposed that the contribution of CSA to the solubility of PPy doped with mixed acid is to decrease the interaction among PPy chains due to the large molecular size of CSA, while DBSA contributes to the solubility by its good solvating effect derived from its long alkyl chain. These may be a reason that both the solubility and conductivity of PPy are improved by the presence of CSA compared with those of PPy doped only with DBSA.