The influence of organic loading rate (OLR) on a two stage integrated bioreactor was investigated in this study. The bioreactor consisted of two biological zones (aerobic and anoxic), a clarifier after the biological zones and an effluent zone, operated as a unit compartmental post-anoxic system. The aerobic zone was integrated into the anoxic zone and the anoxic zone was integrated into the clarifier. A 10 layer hollow rectangular and circular acrylic made submerged materials were installed in the aerobic and anoxic zones, respectively. Asynthetic wastewater simulating a low and medium strength domestic wastewater with biochemical oxygen demand (BOD) concentration of 115 and 260 mg/L, corresponding to two different OLR of 0.33 kgBOD5/m3/m2.d�1 (phase 1) and 0.75 kgBOD5/m3/m2.d�1 (phase 2), was used at a fixed HRT of 12 days. The performance of the bioreactor was monitored by the BOD5 removal. Results show that BOD5 removal was stable at 97.3 with increasing OLR from 0.33 kgBOD5/m3/m2.d�1 in phase 1 to 0.75 kgBOD5/m3/m2.d�1 in phase 2. The BOD5 removal rate increased from 0.314 kgBOD5/m3/m2.d�1 in phase 1 to 0.73 kgBOD5/m3/m2.d�1 in phase 2. However, the residual effluent concentration increased from 3 to 7 mg/L with increasing OLR. The aerobic zone was more prominent for BOD5 removal throughout the study. NH+ 4 -N and NO3-N was also monitored and was found to reach 98 and 73 removal in phase 2. This study, therefore shows that OLR did not cause any decrease of the bioreactor performance at the operating conditions investigated. © 2016 Taylor & Francis Group, London.