We report the effect of rGO on structural, electrical, spectral and nonlinear optical properties of reduced graphene oxide-polyaniline (rGO-PANI) nanocomposites. The rGO-PANI composites with different concentration of rGO were synthesized through an in situ polymerization method. The structural and optical studies of the composite powders show that the template effect of rGO provides a well ordered structure of PANI with better crystallinity. This may be due to the strong electrostatic, p–p, and hydrogen bond interactions between PANI and rGO materials. The conductivity of the composite material increases with respect to pure PANI up to a particular limit, and then decreases. It is mainly due to the disordered conjugated structure of PANI. The nonlinear optical properties of rGO–PANI composites are evaluated by Z-scan technique using a continuous wave Nd:YAG laser at a wavelength of 532 nm. Two photon absorption is the main mechanism behind the self defocusing nature of rGO - PANI composites. The saturable absorption behavior of the material is due to the depletion of valence band and the band filling effect of sp2 carbon domains. The nonlinear absorption coefficient and refractive index of the samples are also estimated and the results show that rGO-PANI composite material is a promising candidate for the applications in optical switching, optical sensors and in ultrafast photonics. © 2019 Elsevier Ltd. All rights reserved.