Ba_3−xSr_xM₄Ti₄O₂₁ (M = Nb, Ta and 0≤x≤3) ceramics have been prepared through solid state ceramic route. The structure and microstructure of the compositions have been studied using powder X-ray diffraction and Scanning Electron Microscopic studies. In the present study, both Ba₃Nb₄Ti₄O₂₁ and Ba₃Ta₄Ti₄O₂₁ are obtained as single phase compositions whereas strontium rich compositions exhibit multiphase in nature. Energy dispersive X-ray analysis has been performed to identify the nature of additional phases present in the strontium rich compositions. The dielectric constant, dielectric loss and temperature variation of dielectric constant of the well sintered ceramic specimens have been studied in the low frequency region (<13 MHz) using an impedance analyzer. The present study reveals that high dielectric compositions can be realized by Sr-substitution in the BaO–TiO₂–Nb₂O₅/Ta₂O₅ ternary systems.