A study of anaerobic treatment of fermentation mother liquid of monosodium L-glutamate with high chloride ion concentration was carried out using a laboratory-scale UASB reactor. The reactor was seeded evident inhibition performance when the chloride ion concentration was below 4500mg/L, while inhibition level obtained at a chloride ion concentration of 5000mg/L, however, a preferable COD removal rate could be achieved after acclimation. The average COD removal rate could be above 80% when the chloride ion concentration was as high as 8000mg/L..