A lab-scale up-flow anaerobic sludge blanket (UASB) reactor was used for biogas production from the citrus juice process wastewater (CPWW). The volume of the reactor was 11.5 L. During 200 days of the reactor, the organic loading rate (OLR) value changed from 1.8- 21.9 kgCOD./m3.d, upflow velocities (Vup) 0.1–5.2 m/h and hydraulic retention time (HRT) changed from 0.042 to 4.16 days. The reactor showed a stable performance at all organic loadings. Experimental chemical oxygen demand (COD) removal efficiencies were 71.5±21% and 83.3±16.3% for total COD (TCOD) and soluble COD (SCOD), respectively. The acetic acid concentration changed from 135 to 650 mg/L. The temperature was kept in the range of 35.1±1.4 oC, the pH in the range of 6.6±0.2, and the alkalinity was controlled daily and kept in the range of 411±273 CaCO3 mg/L. After anaerobic reactions, 6283±3476 m3/d biogas was produced and the methane concentration in the biogas was 65.5±11.5%. Depending on the methane production, the annual energy value potential that can be obtained from the existing UASB reactor is estimated as 48,768 kWh.