<p>This study aims to develop AC/Fe₃O₄/K₂CO₃, a stable and sustainable heterogeneous magnetic catalyst made from local biomass waste, for the synthesis of biodiesel from waste cooking oil (WCO). This study investigates the development of a bifunctional catalyst derived from local biomass waste, specifically palm fruit shells (<i>Arenga Pinnata Merr.</i>), magnetite, and potassium carbonat. The catalyst was synthesized through carbonization followed by chemical activation and impregnation. The activated carbon/Fe₃O₄/K₂CO₃ composite was characterized using X-Ray Diffraction (XRD) to assess its crystallinity and phase identification, FTIR to identify the chemical components in the material, SEM-EDX to analyze the morphology and elemental composition, and VSM to determine the magnetic properties. All of these characterizations indicated successful composite formation with nanoparticle magnetite (Fe₃O₄) and base sites (K₂CO₃), confirming structural integrity and potential catalytic properties of the material. The catalyst demonstrated high efficiency in converting waste cooking oil (WCO) into biodiesel, achieving a yield of 96.56% within just 30&#xa0;min at a relatively low temperature of 60&#xa0;°C, using a methanol-to-oil molar ratio of 1:6 and 3%wt catalyst load. The produced biodiesel was analyzed using FTIR and GC-MS. The results indicate that the activated carbon/Fe₃O₄/K₂CO₃. The mechanism of activated carbon/Fe₃O₄/K₂CO₃ transesterification is further examined in the work, and the catalyst’s repeatability is evaluated. Activated carbon/Fe₃O₄/K₂CO₃ showed good stability and reusability, sustaining an 86.18% biodiesel production after 5 cycles. catalyst may function as a feasible substitute for conventional catalysts, providing enhanced product separation and catalyst recovery, which are critical for economical biodiesel synthesis. This research advances the development of sustainable and efficient biodiesel synthesis technologies by exploiting local waste biomass and minimizing environmental effects.</p>