Abstract: Enzymatic hydrolysis of penicillin G（Pen G）into phenylacetic acid（PAA）and 6-aminopenicillanic acid（6-APA）suffers not only substrate inhibition and non-competitive inhibition by 6-APA，but also competitive inhibition by PAA.In the industrial process，PAA is generally eliminated by addition of aqueous ammonia to form soluble ammonium salt，which generates industrial waste.Extractive biocatalysis is a potential method to overcome the above obstacles and might be even directly used in enzymatic hydrolysis of penicillin G from fermentation broth.The partitioning behavior of Pen G hydrolysis reactants and the stability of immobilized penicillin acylase in cloud point system，a novel extractive bioreaction system，were determined.It suggests that cloud point system might be a novel extractive bioreaction system for the industrial process of penicillin hydrolysis.