Anaerobic digestion (AD) has been known as a feasible process for the conversion of organic waste to biogas. This research aimed to study the performance of an internal circulation (IC) anaerobic reactor treating food processing wastewater under different organic loading rates. The experiment was carried out in a lab-scale of IC reactor at ambient temperature. The reactor was made of poly-methyl methacrylate with dimensions of IC reactor had 1.8 m in height and square surface with 0.12 m in width, the working volume was 25 L. After the acclimation period, the reactor was run for 72 d which was divided into four stages corresponding to four levels of organic loading rate (OLR) as 5; 10; 15 and 20 kg COD m-3 d-1. During the experimental period, influent and effluent supernatant was sampled daily and analysed such chemical parameters of pH, TSS (Total suspended solids), COD (Chemical oxygen demand), TN (Total nitrogen), TP (Total phosphorous), biogas volume to evaluate the performance of IC reactor. The result showed that OLR had a significant effect on the removal of organic and nutrient matters in IC reactor. At each level of OLR, the removal efficiency was low at the start and gradually improved to become stable at the end of the phase. IC reactor was good at COD removal and achieved the maximum removal rate 85.4 % at OLR as 10 kg COD m-3 d-1. When OLR increased to 15 and 20 kg COD m-3 d-1, the reactor could perform stably at maximum COD removal as 84.3 % and 72 %. The maximum biogas production rate was achieved as 93.8 L day-1 at day 72nd of the experiment. This study suggests that IC anaerobic reactor is applicable for the removing of organic matter in wastewater at high organic loading rate.