In this paper, attention is drawn to the effective mechanical and electrical properties of swollen semicrystalline ethylene-co-butyl acrylate (EBA) polymer filled with spherical carbon black (CB) nanoparticles. The kinetics of solvent diffusion is studied at room temperature by immersion of dried samples with different CB volume fractions in toluene. Solvent diffusion into the composite samples follows power law dependence as a function of time and is characterized by a decrease in solvent uptake with increasing the CB particles acting as barriers. The preferential localization of solvent molecules into the composite is examined by evaluating the wetting coefficient. The stress-strain curves of pre- and post-swelling obtained by uniaxial tensile tests show a decrease in Young's modulus, yield stress and strength of the swollen samples compared to the unswollen ones. Haward and Tackray's model is used to describe the physics of the stress-strain curves of both unswollen and swollen samples in relation to the microstructure characteristics (entanglements, strain hardening modulus). It is found that the dc electrical conductivity of swollen samples is several orders of magnitude lower than that of unswollen samples.