Cell surface hydrophobicity and charge are determining factors for the demulsification ability of a bacterial demulsifier. This research provides an effective method for adjusting the surface properties of demulsifying cells with oleic acid (OA)-coated magnetic nanoparticles (M-OA) to enhance its demulsification performance. A series of M-OAs with different surface properties was synthesized. Magnetically responsive demulsifying bacteria (MRBD-Os) were obtained by combining the M-OAs with demulsifying bacteria (Alcaligenes sp. S-XJ-1). The water contact angle and charge of the MRBD-Os were in the range of 89-115 degrees and -35 to -30 mV, respectively. The results indicated that MRBD-Os all showed better demulsification performance than demulsifying bacteria alone. At a water contact angle of 105 degrees the demulsification rate of MRBD-Os was 33% higher and the transmitted light intensity of separated water was increased six-fold compared with those of the bacteria without M-OAs. Surface hydrophobicity improved the translocation of demulsifying bacteria to the interface, resulting in enhanced droplet coalescence. Surface charge influenced cell aggregation on the interface. The enhancement of bacterial demulsification performance using magnetic nanoparticles may be useful in future applications. (C) 2017 Elsevier Ltd. All rights reserved.