Structural properties, electric impedance, electric modulus and dielectric spectra properties have been used to investigate a Polyaniline/Manganese dioxide (PANI /MnO2) nanocomposites prepared by in situ polymerization method. Prepared nanocomposites were analyzed by AC impedance spectroscopy. Pure PANI and MnO2 nanoparticles have good crystalline nature, but when it was prepared to nanocomposites, crystalline nature could be change. When the concentration of MnO2 nanoparticles has increased in nanocomposites, crystalline behaviour has been increases. Impedance studies were used to explain the electrode process. The modulus data of nanocomposites were analyzed as a function of different frequency range at a particular temperature. At low-frequency range, all the values of a real part of the electric modulus remain almost near to zero. Dielectric constant and dielectric loss have explained in brief. The impedance analysis was confirming the non-debye nature of the materials