[en] Ca²⁺ and Nb⁵⁺ co-doped multiferroics having composition Bi_0.8Ca_0.2Fe_1−xNb_xO₃ (x = 0.00, 0.05, 0.07, and 0.10) were synthesized via solid-state reaction method. Effect of substitution was analyzed by structural, electrical and magnetic measurements of modified BiFeO₃ multiferroics. The samples were characterized by X-ray diffraction (XRD), and results support that impurity phases, which normally occurred in BFO, were significantly diminished in modified BiFeO₃. Rietveld refinement of XRD patterns demonstrates that phase transformation occurred in all prepared samples. Structure symmetry gets disturbed in presence of Nb and mixed phase (rhombohedral (R3c space group) and orthorhombic phase (Pbnm space group)) was confirmed by refinement. The studies of dielectric, impedance and electrical properties at a wide range of temperature and frequency offered us noticeable information of Nb substitution. Frequency dependence impedance confirms the non-Debye type of relaxation. Nb doping increases resistivity and samples show polarization hysteresis loop. All samples show ferromagnetism in modified multiferroics with maximum remanent magnetization is M_r = 0.0581 emu g⁻¹ and coercive field is H_c = 4.7505 kOe for x = 0.10 which is ten times of magnetization observed in parent sample. Co-substitution at A and B site is responsible for phase transformation and enhancing electrical and magnetic properties. - Highlights: • Ca²⁺ and Nb⁵⁺ co-doped BiFeO₃ shows improved magnetic structure. • Crystal structure has been analyzed using Rietveld refinement. • Multiferroic properties are also improved.