Poly(o-phenylenediamine) ferrite nanocomposites (PoPD/NiFe2O4) with different ratios of NiFe2O4 nanoparticles (10%, 20% and 30%) were synthesized by in-situ chemical oxidative polymerization method. NiFe2O4 nanoparticles were prepared by auto-combustion method using urea as fuel. The PoPD/NiFe2O4 nanocomposites were characterized by FTIR and XRD, SEM, TEM and thermogravimetric analysis. The FTIR and XRD pattern ascertain the interaction of PoPD with NiFe2O4 nanoparticles. The spherical morphology of PoPD is affected by the incorporation of NiFe2O4 nanoparticles. Magnetic properties of PoPD/NiFe2O4 nanocomposites were analyzed by using vibrating sample magnetometer. The hysteresis loops of NiFe2O4 and PoPD/NiFe2O4 nanocomposites exhibited ferromagnetic nature at room temperature. Dielectric properties of PoPD/NiFe2O4 nanocomposites at different temperatures have been carried in the frequency range from 50 Hz to 5 MHz. The ethanol gas sensing property of PoPD/NiFe2O4 nanocomposites was studied at room temperature using PMMA fiber optic method. © 2017, Springer Science+Business Media, LLC, part of Springer Nature.