This study developed an effective combined UF-NF membrane system for ultrafiltering erythromycin fermentation broth and concentrating the filtrate to improve the downstream efficiency. Three membranes with MWCO of 100, 30 and 10 kDa respectively were tested for ultrafiltration work. 30 kDa membrane was then selected due to its good performance by giving the highest permeation flux, satisfying permeate quality, high volume concentration factor (VCF=3.9) and high yield (98.9%). The optimal diafiltration factor (DF) for ultrafiltration is between 2.0 and 2.5. The basicity of UF permeate was found to be adverse to the NF concentration. At pH of 7-7.5, obvious enhancement of flux (>30 I/m(2) h) and VCF (about 4.0) were achieved for NE NF concentrates can be extracted targeting erythromycin concentration of higher than 40,000 U/ml with good extraction efficiency, which is about 1.5% higher than that of filter press filtrate. With this technology, the usage of exacting solvent and cle-emulsifier will be greatly minimized, reducing the load on the followed high speed centrifuge, solvent recycle and treatment of waste solids and wastewater. Moreover, NF permeates could be recycled directly as UF diafiltration water, extensively reducing the consumption of water and the load on wastewater treatment. V 2008 Elsevier B.V. All rights reserved.