Usually, oily wastewater produced from polymer flooding was treated by cationic flocculant in oilfield. In this paper, non-ionic demulsifiers based on polyethyleneimine (PEI) with various ethylene oxide and propylene oxide contents were synthesized. The performances of these PEI demulsifiers were studied. The results indicated that most of the PEI products could perform as well as the cationic flocculant, when the temperature was up to 55 degrees C. This phenomenon may be explained by hydrophilic-lipophilic deviation (HLD) theory. When temperature increased and moved to phase inversion temperature, the HLD of oil-PEI demulsifier-water system moved to zero and the stability decreased. After stirring, the emulsion was decomposed. In addition, the effects of dosage, stirring speed and stirring time on the treatment of PEI11 and PEI231 were also studied. (C) 2014 Elsevier B.V. All rights reserved.