This work deals with the anaerobic digestion using up flow anaerobic sludge blanket (UASB) reactor to treat a mixture of food waste and domestic wastewater to generate renewable energy biogas (methane). The reactor was operated under the conditions of mesophilic temperature (35°C), pH 6.5 (controlled by the addition of 3,500 mg/L calcium carbonate), and 10 days of hydraulic retention time (HRT). The sludge maturation and granulation process was achieved in 40 days with a stable biogas production (0.71 L/d) with methane content and yield of 54% and 0.214 L CH₄/g COD removed respectively. When the reactor was fed continuously with a mixed wastewater at the organic loading rate of 2 g COD/L/day, the chemical oxygen demand (COD) removal efficiency and the methane content were 80% and 56%, respectively, within 3 days of the reactor operation. The methane content, however, dropped to 37% due to the accumulation of long chain fatty acids (LCFAs), subsequently promoting the sludge wash out and inhibiting the methanogenic activity. When the reactor was operated in the intermittent feeding mode (48 h feed/48 h feed less) at 10-day HRT, the intermittent mode promoted the degradation of fatty matters more efficiently and the inhibition observed in the continuous mode could be recovered accordingly.