Electrically conducting polyaniline/multiwalled carbon nanotubes (PANi/MWCNTs) nanocomposites were successfully synthesized via chemical oxidative polymerization. For this purpose, PANi was first prepared in an aqueous acidic medium, hydrochloric acid (HCl), at various temperatures to determine the proper polymerization temperature and to prepare the polymer with the highest electrical conductivity. For nanocomposite preparation, the polymerization of aniline (ANi) was carried out in the presence of various amounts of MWCNTs dispersed using a proper surfactant. The effect of HCl and MWCNT contents on the conductivity of the resultant composites was investigated. The results showed that the conductivity was monotonically increased with increasing the MWCNT and HCl levels. In addition, the effect of anionic and cationic surfactant type, sodium dodecyl sulfate (SDS) and cetyltrimethylammonium bromide (CTAB), on the conductivity and morphology of the resulting nanocomposites, was studied. Fourier transform infrared (FT-IR) spectroscopy, Raman spectroscopy, two- and four-point resistivity measuring methods, and field emission scanning electron microscopy (FESEM) were used to characterize the neat PANi and PANi/MWCNT nanocomposites. The conductivity variation of the conducting polymers versus elapsed time was investigated to determine the intensity and dominant aging mechanism. Electromagnetic shielding properties of the conducting nanocomposites were also studied. The results indicated that the nanocomposite with the highest MWCNTs level absorbed more than 83% of the incident electromagnetic waves.