The new water-soluble self-acid-doped conducting polyaniline, poly(aniline-co-N-propylbenzenesulfonic acid-aniline) (PAPBSAH), is synthesized, in which 47% of total nitrogen is linked with -(CH2)(3)-< O >-SO3H groups as determined by elemental analysis. The protons in the pendent acid groups are capable of doping the nitrogen atoms in the quinoid units. The conductivity of the cast film (at 25 degrees C, 8.5 x 10(-5) S cm(-1)) increases with temperature and reaches the maximum at 125 degrees C (4.7 x 10(-4) S cm(-1)); it then decreases with temperature to 160 degrees C (1.7 x 10(-4) S cm(-1)). This polymer has better thermal stability than its parent polymer, poly(aniline-co-N-propanesulfonic acid-aniline), in which the pendent group is -(CH2)(3)-SO3H and its maximum conductivity is located at 110 degrees C.