Extraction of erythromycin from fermentation broth using salt-induced phase separation processes has been examined, In this process, the fermentation broth was first mixed with organic solvent acetonitrile to form a homogeneous mixture. Then the mixture was separated into two phases by adding an inorganic salt. such as NaCl, Na2SO4. Accompanying phase separation, erythromycin was extracted from broth to organic phase. Erythromycin was recovered finally from solvents by vacuum distillation and crystallization, The phase equilibrium of water-acetonitrile systems was determined at different salt concentrations. The extraction yield and partition coefficients of erythromycin were measured at different operative conditions. It was found that comparing with traditional liquid-liquid extraction, the new extraction processes have advantages of the extraction efficiency high and phase separation rapid, The extraction efficiency was more than 98.5% by one-stage extraction. The chemical titer of erythromycin was over 930 mug/mg. The yield of erythromycin was over 70%.