<p>This study evaluates the potential of fish oil, extracted from Pangas (<i>Pangasius pangasius</i>) fish waste, as a sustainable fatliquoring agent in leather processing. Extraction with ethanol medium yielded 14.54% fish oil, compared to 12.30% with water. Upon sulfation, distinct FTIR peaks at 1160 cm⁻¹ and modifications to the –OH band confirmed successful chemical transformation. Physicochemical analysis revealed increased acid value (11.22 mg KOH/g), saponification value (200.52 mg KOH/g), and specific gravity (0.93) for the sulfated fish oil. TGA analysis demonstrated significant stability, with around 20% residue retained above 400 °C, reflecting the robustness of the modified oil. Compatibility tests of sulfated fish oil fatliquor emulsion demonstrated stability in various aqueous, alkaline, and saline conditions, except under strong acid (10% H₂SO₄), where breakdown occurred. It also exhibited a hydrodynamic diameter of 342.3 nm and a zeta potential of −83.0 mV, highlighting the dispersion efficiency and electrostatic stability of the sulfated emulsion. Mechanical performance of leather processed with 4% fish oil fatliquor surpassed conventional fatliquoring agents, delivering tensile strength of 24.60 N/mm², stitch tear resistance of 98.04 kg/cm, and grain crack load of 42.62 kg, alongside reduced surface defects under SEM imaging. Environmental impact assessment further validated the sustainability of this approach, as effluent from fish oil fatliquor treatment exhibited lower BOD, COD, and TDS values than those associated with commercial alternatives. Collectively, these findings position sulfated fish oil as a high-performing, eco-friendly fatliquoring agent capable of improving both leather quality and environmental outcomes.</p> Graphical Abstract <p></p>