Cooking oil waste is a common by-product from households, restaurants, and food industries, and its improper disposal can cause severe environmental pollution. Repeated use of cooking oil leads to chemical degradation through oxidation, hydrolysis, and polymerization, resulting in darkening, off-odors, elevated free fatty acids (FFAs), and increased peroxide values, posing potential health and environmental risks. This study aimed to investigate the purification efficiency of coconut shell-derived activated carbon in reducing free fatty acid contents and improving oil quality parameters, including pH, calorific value, viscosity, and density. Activated carbon was produced by carbonizing coconut shells at 450 °C for 3 hours under limited oxygen using a lab-scale pyrolysis reactor. The resulting charcoal was then chemically activated with KOH, washed to a neutral pH, dried, and ground to ≤250 µm. Adsorption experiments were performed by adding 2.5% (w/w) activated carbon to 450 ml of cooking oil waste and stirring at 600 rpm for contact times of 30, 60, and 90 minutes. The treated oil was filtered using Whatman No. 1 filter paper (110mm diameter) and analyzed for FFA, pH, calorific value, viscosity, and density. Our results showed that the FFA content decreased significantly from 0.286% to 0.049% (82.9% reduction) with increasing contact time, while the pH improved from 4.62 to 5.91, indicating effective removal of acidic degradation products. The calorific value increased slightly from 8981 to 9019 Cal/g, suggesting removal of oxidized and polar compounds. The purified waste cooking oil, with reduced acidity and improved pH, is suitable for biodiesel production and non-food industrial applications, demonstrating potential for circular economy implementation.