This work focuses on the effect of ionic radius of dopant cations on the structural and electrical properties of different rare earth doped ceria based nanoparticles. The lattice parameter of the doped samples increases linearly with dopant ionic radius. The Gd3+ doped ceria shows minimum r.m.s. strain among the others. The conductivity and activation energy of the samples are significantly affected by the dopant ionic radius. The Gd3+ doped ceria shows highest conductivity and lowest activation energies among the other rare earth doped ceria. The conductivity decreases and activation energy increases for the dopants having ionic radii higher and lower with respect to Gd3+. The ion movements at grain and grain boundary are also found to depend on the ionic radius of the dopants. Scaling of frequency dependent modulus spectra reveals the temperature and ionic radius independent relaxation mechanism. The dielectric constant shows that the stability of defect associates is higher for the samples having ionic radius lower and higher than the ionic radius of Gd3+ ions. The conductivity values are well supported by the VRH model.