Zn-Co ferrites doped with Er³⁺ and Pr³⁺ with different concentrations were synthesised by co-precipitation method at constant calcination temperature. XRD results show an increase in the lattice parameter. Particle sizes determined from TEM are close to those determined from XRD, confirming PVP acts as controlling of the nanoparticles growth. Electron paramagnetic resonance (EPR) spectra analysis indicates that the spin-spin relaxation time T₂ increases and the g-factor decreases with increasing Er³⁺ and Pr³⁺ content. The saturation magnetisation and the coercivity decrease with increasing RE³⁺ content. The dielectric constants ε’ and ε” and the dielectric loss tangent (tanδ) decrease, and the a.c. conductivity increases with the increase of Er³⁺ concentration between 0.00 wt% and 0.20 wt%; the same trend is observed for samples doped with Pr³⁺ of concentrations 0.04, 0.12 and 0.20 wt%, while that doped with 0.08 wt% of Pr³⁺ shows a peak at low frequency.