Polypyrrole (PPy) with microstructure was prepared in sodium dodecyl benzene sulfonate (SDBS) aqueous solution. The composition, morphology, structure and thermostability of the resulting PPy particles were collected by elemental analysis, scanning electron microscopy (SEM), fourier transformation infrared (FT-IR) spectra and differential thermal analysis (DTA). The yield and conductivity were also measured. Different preparation conditions including the concentration of the surfactant and the monomer, addition of acid or not and the kind of the oxidant were all investigated. The results showed there was an extrinsic relation between the morphology and the thermostability of the samples. Based on the relation, a possible mechanism was proposed that there might be two kinds of interaction between SDBS and PPy, i.e., inter- and intra-interaction.