Nanofibers of polypyrrole have been synthesized by sonochemical method in the presence of a structure directing agent, i.e. dodecyl benzene sulphonic acid (DBSA). The length of the fibers is seen to increase significantly from similar to 13 nm to greater than similar to 1700 nm, while the diameter is similar to 13-17 nm, respectively. The reaction was carried out under ambient conditions by varying the concentration of pyrrole (0.001-0.1M), ammonium persulphate (0.0075-0.02M), and DBSA (0.05-0.2-M). However, the formation of fibers is observed at a specific ratio of 1 : 0.5 : 5. The UV-vis spectra exhibit a sharp peak at a wavelength of similar to 490 nm corresponding to the polaron band indicating the formation of polypyrrole. The X-ray diffractogram shows a broad peak in the 20 range of similar to 10 degrees-30 degrees and two sharp peaks at similar to 31 degrees and 32 degrees confirming the formation of polypyrrole. The morphological analysis of the sample have been carried out by transmission as well as scanning electron microscopy which reveals the formation of extraordinary long fibers having the length extending to more than similar to 1700 nm. (C) 2008 Wiley Periodicals, Inc.