The production of microbial biomass protein (MBP) and fungal α-amylase from starch processing wastewater (SPW) by a selected strain Aspergillus oryzae was investigated as part of a comprehensive SPW treatment programme. A simple, non-aseptic, one-stage process was successfully carried out by using an air lift bioreactor under the optimised growth conditions at pH 5·0 and 35°C. Bioproduct yields of 6·1 g/litre of MBP that contained 38% protein, and 55 EU/ml of α-amylase enzyme were obtained from a 12-h batch culture. The pellet bioproduct led to easy harvesting of the biomass protein. The SPW was treated by removing 95% COD, 93% BOD and 98% suspended solids, and can be used for farm irrigation. The α-amylase had a stable enzyme activity at pH 5–9 and 25–35°C. Pretreatment by hydrolysis and sterilization of SPW, and nutrient supplementation may be unnecessary.