This study investigated the synergistic effect of anaerobic co-digestion (ACoD) of food waste (FW) and domestic wastewater (DWW) together with the magnesium (Mg) supplement on biogas production and organics removal. An upflow anaerobic sludge blanket (UASB) reactor was operated at 35 °C under an intermittent feeding mode (48 h feed and 48 h no feed) while batch experiments were performed for the effect of Mg supplement on ACoD. In terms of chemical oxygen demand (COD) removal and methane recovery, the best performance was at 150 mg/L Mg supplement where COD removal efficiency and methane content reached 83.1 ± 1.1 % and 61.4 ± 0.6 %, respectively, 13.06 % and 10.63 % higher compared to the control without Mg supplement. In addition, a lower ammonia-nitrogen accumulation (661.1 ± 53.0 mg/L) was observed compared to the control (811.0 ± 44.5 mg/L), showing the Mg supplement also stimulatory to the ammonia-nitrogen removal, further reducing the inhibitory effect of ammonia on the ACoD performance. Results imply a promising strategy for the successful implementation of the use of ACoD technology to the treatment of FW and DWW for the resource recovery.