An electrochemical sensor based on in situ synthesized Cu2O microparticles-Cu2O nanowires-graphene (Cu2O MPs-Cu2O NWs-graphene) composite for sensitive detection of ethylenediamine (EDA) is reported. X-ray diffraction, X-ray photoelectron spectroscopy, field emission scanning electron microscopy, field emission transmission electron microscopy, and energy-dispersive X-ray spectroscopy were utilized to characterize the composition and morphology of the composite. The electrochemical behaviors of EDA at the Cu2O MPs-Cu2O NWs-graphene composite modified electrode were investigated by electrochemical impedance spectroscopy, cyclic voltammetry, and linear sweep voltammetry. The electrochemical sensor exhibited excellent analytical performance for EDA detection with low detection limit of 3.83 x 10(-5) M (S/N = 3) and a reproducibility of 1.1 % relative standard deviation. The modified electrode exhibited a rapid response to EDA within 5 s and the amperometric signal showed a good linear correlation to EDA concentration in a broad range from 0.25 to 1.25 mM with a correlation coefficient of R = 0.99699. The superior electrochemical performances of Cu2O MPs-Cu2O NWs-graphene composite are attributed to their peculiar composite structure and the synergistic effects between Cu2O MPs-Cu2O NWs and graphene [Huang et al., Sens Actuators B 178: 671-677, 2013; Luo et al., Anal Chim Acta 709: 47-53, 2012].