In this study, ferrite-based Zn–Ni–Fe magnetic powders were incorporated into a PLA matrix at 10 wt.% and 20 wt.% to fabricate composite filaments, which were subsequently used to produce toroidal cores via the fused filament fabrication (FFF) method. Both commercially available ferrite powders and ZnNiFe powders synthesized through a sol-gel assisted solution combustion method were employed as fillers. Prior to compounding, the powders were calcined between 600 °C and 1000 °C to promote phase development and crystallinity. The composite filaments were prepared using a twin- screw extruder to ensure homogeneous dispersion of the magnetic fillers. Toroidal cores printed from these filaments were evaluated in terms of magnetic performance using a custom-built test circuit comprising a signal generator and digital oscilloscope operating at 1 kHz and 100 kHz. As a reference, a commercial 40R 100 MHz ferrite toroidal core (17.5 × 6.35 mm) was used under identical conditions. Clear and undistorted signals were obtained only from the reference core, while printed samples with 10 wt.% and 20 wt.% filler showed weak or distorted responses. This behavior is attributed to the lack of magnetic continuity and insufficient grain-to-grain contact within the printed structure. The study emphasizes the need for microstructural optimization in additively manufactured toroidal inductor cores.