Abstract.An investigation of clavulanic acid behavior in an aqueous two-phase micellar system employing the surfactants n-decyltetraethylene oxide (C 10 E 4 ) and dodecyldimethylamine oxide (DDAO) was carried out. According to the results, clavulanic acid partitions evenly between the two phases of DDAO micellar system, mixed DDAO-C 10 E 4 micellar system, as well as C 10 E 4 micellar system. Therefore, electrostatic interactions between positively charged DDAO-containing micelles and negatively charged drug were not strong enough to influence the partitioning. Nevertheless, clavulanic acid extraction from Streptomyces clavuligerus fermentation broth in C 10 E 4 micellar system employing a previous protein denaturation step provided recovery of 52% clavulanic acid with removal of 70% of the contaminant proteins, which is already promising as a purification strategy.