Propagation properties of plasma-filled PPWG surrounded by BP layers are explored in this research. Field equations are derived with the help of Maxwell’s equations. Boundary conditions x = d / 2 and x = − d / 2 are applied to obtain the characteristic equation for transverse magnetic (TM) mode. The influence of plasma frequency, electron doping, number of BP layers and core width on effective mode index are analyzed for armchair and zigzag conductivity of BP in the THz frequency range. It is concluded that armchair conductivity has a higher effective mode index compared to the zigzag conductivity of BP for the proposed waveguide structure. The presented results may have potential applications to fabricate black phosphorus-based nanophotonic devices in the THz frequency range.