Activated carbon-Fe3O4 composite was successfully synthesized. This work aimed to synthesize magnetic activated carbon and study its performance as a gasoline adsorbent. Dried coconut shells were pyrolyzed using a microwave to produce activated carbon (AC). The activated carbon-Fe3O4 composite was synthesized by the co-precipitation method, resulting in AC-M. Contact angles of AC-M with three different kinds of liquid were calculated using Drop Analysis LB-ADSA plugin in the ImageJ application program. Contact angles between AC-M with water, gasoline-water mixture, and gasoline were 84.156 ˚, 72.928 ˚, and 0 ˚, respectively. The contact angles show the hydrophobic properties of the composite. The adsorption capacity of AC-M for gasoline adsorption was 1252.22 mg/g for adsorption time 4 min and mass of adsorbent 0.09 g and followed the adsorption kinetic pseudo-second-order model from Ho and McKay with adsorption rate constant 0.0012 g/mg/min.