Highly crystalline polyaniline (PANI) nanotubes and nanofibers ca. 80-170 run in diameter are successfully prepared by a micelle soft-template" method in the presence of dicarboxylic acids dopants with different numbers (n) Of -CH2- groups (n = 0-4). It is found that the diameter of the nanostructures increases on increasing the number of -CH2- groups in the dicarboxylic acids. The conductivity of the nanostructures increases as their diameters decrease, showing that size has an effect on conductivity. A narrow peak at 2 theta = 6.50 degrees is observed in the X-ray diffraction pattern, indicating that the distance in the direction perpendicular to the polymer chain increases as the number of -CH2- groups increases.