Here, we demonstrate the utilization of calcined jackfruit seeds as highly effi cient heterogeneous base catalysts (JSC-400 and

JSC-600) for biodiesel synthesis from soybean oil. Catalysts were characterized by PXRD, FTIR, N

2 -adsorption, SEM–EDX,

FETEM, XPS, Hammett and CO 2 -TPD techniques. PXRD and FETEM analysis confi rmed the presence of mixed metals

in their oxide and carbonate forms, and their polycrystalline structures, respectively. FESEM and N

2 -adsorption revealed

the spongy, fl ake-like morphology and mesoporous structure of the catalysts. The concentration of potassium (K) in JSC-

400, which is responsible for its basicity, was evaluated using EDX (12.40 atomic%) and XPS (13.87 atomic%). JSC-400

showed a more promising biodiesel yield (97.7%) in 30 min, which might be due to the higher basicities of JSC-400 with

11.51, 0.42 mmol/g and 1.997 mmol/g than JSC-600 (11.51, 0.42 mmol/g and 1.997 mmol/g) as measured by pH, Hammett

and TPD-CO 2 techniques, respectively. Three times consecutive recycle study of JSC-400, showed no signifi cant loss in

yield (95.2%), compared to fresh catalyst (97.7%). Thermodynamic and kinetic studies confi rmed the non-spontaneous and

pseudo-fi rst order reaction, respectively. Product was confi rmed by FTIR, 1 H and 13 C NMR and GC–MS techniques, and

fuel properties were found to be comparable with the literatures and international standards.