A method suitable for isolation of neutral proteinase(NP) and oxytetracycline (OTC) from Streptomyces rimosus culture has been developed. In an aqueous two-phase system consisting of PEG-6000 and ammonium sulfate (AMS), all cell debris and the major part of proteins and OTC were partitioned. Neural network mode! for describing liquid - liquid equilibria in two phase aqueous solutions was developed. Multilayer feedforward artificial neural network was used and trained applying backpropagation algorithm. The models adequacy was verified by comparing experimental and computed neutral proteinase and OTC concentration in extract and rafinate.