A straightforward, template-free chemical oxidative polymerization of aniline was used to prepare nanofibrillar polyaniline (nf-PANI) and a set of corresponding composites with multiwall carbon nanotubes (MWNTs). All the products showed remarkable water dispersibility since they are formed by hydrophilic particles of nanometric size. A comparative Study performed oil composites in a wide range of MWNT loadings has led to two main Conclusions: oil one hand, the presence of MWNTs affects neither the chemical structure nor the crystallinity of polyaniline. On the other hand, even small amounts of MWNTs have a significant effect on the morphology of polyaniline in composites. This effect is noticeable not only in electron microscopy images but also in the UV-vis absorbance of water dispersions and electrical conductivity behavior in the solid state. Competition between nucleation sites during polymerization is proposed its an explanation for these phenomena.