A highly sensitive o-phenylenediamine (OPD) sensor based on a Fe3O4 doped with functionalized multi walled carbon nanotubes (Fe3O4@f-MWCNTs) composite fabricated glassy carbon electrode (GCE) was developed. The modified Fe3O4@f-MWCNTsIGCE showed an enhanced current (I-pa) response toward OPD relative to that of a Fe3O4/GCE, f-MWCNTs/GCE, and a bare GCE. Under optimum conditions, the Fe3O4@f-MWCNTs/GCE showed a wide linear range remove at OPD concentrations of 0.6-80 mu M. The limit of detection and sensitivity of the f-MWCNTs/GCE, Fe3O4/GCE sensor were found to be 50 mu M, and 2.8002 mA mM(-1) cm(-2), respectively. The developed sensor showed excellent accumulation time, good repeatability, and operational stability. The obtained results suggest that the development of composite could be an effective electro-catalyst and it can play a vital role in biomedical, pharmaceutical, and hazardous free environmental applications. (C) 2017 Elsevier Inc. All rights reserved.