Tubular polypyrrole (PPy) doped with β-naphthalenesulfonic acid (β-NSA) was synthesized by a template-free method. SEM and TEM images proved the tubular morphology. It was found that the morphology of the resulting PPy-NSA was significantly affected by the concentration of β-NSA. When the concentration of β-NSA was increased a variation in the morphology of PPy-NSA of grain–tube–block was observed that was related to the hydrotropic behavior of β-NSA. A growth process of grain–short tube–long tube was observed, and it was assumed that polypyrrole gradually and orderly aggregated to form tubular PPy-NSA due to the acidity of the pyrrole monomer. Elemental analysis, FTIR and X-ray diffraction characterized the molecular structure of the resulting PPy-NSA. It was shown that the polymer main chain of the tubular PPy-NSA was identical to that of PPy synthesized by a common method. The differences in tubular formation mechanism and crystallinity between polyaniline (PANI)-NSA and PPy-NSA microtubules were discussed based on the basicity or acidity of the pyrrole and aniline monomers.