Abstract: The pretreatment process of propionic acid fermented broth by hollow-fiber membrane was investigated. Different kinds of hollow-fiber membranes were screened，and the separation conditions were optimized. It was shown that the polyvinylidenefluoride microporous hollow-fiber membrane (0.1 μm pore size) was more suitable for this system. When the initial pressure was 0.04 MPa，the absorbance of cell density at 660 nm was less than 0.4，pH value was 6.0 and temperature was 30 ℃，the fermented broth could be better pretreated by this PVDF membrane and an expected result was obtained.