The extraction of penicillin G by ionic liquid [Bmim] PF6 has exhibited promising prospect. The stability of penicillin G is crucial for developing a green ionic liquid-based extraction technology. In this work, the stability of penicillin G in [Bmim] PF6 was systematically investigated. The results showed the stability of penicillin G was significantly influenced by pH and temperature. It tended to be more stable when pH value increased from 1.5 to 4.0 and the temperature gradually decreased. The half-life (t(1/2)) of penicillin G in [Bmim] PF6 was 17.7 h in the optimal technological condition (pH 2.0 and 10 degrees C), which is enough for the requirement of extraction technology. The reaction of penicillinG in [Bmim] PF6 followed the first order kinetics in the pHrange 2.0-4.0. Three isomers of penicillin G were found through rearrangement at pH 2.0, and their structures were not affected by temperature. (C) 2018 The Chemical Industry and Engineering Society of China, and Chemical Industry Press. All rights reserved.