A novel cobalt phosphide (CoxP, a mixture of CoP and Co2P) embedded within nitrogen-doped porous carbon microspheres was facilely prepared by pyrolysis of a composite precursor. The composite precursor was achieved by in-situ growth of Co-based zeolitic imidazolate framework (ZIF-67) on the Zn(PO4)(x) microspheres. The as prepared CoxP decorated nitrogen-doped porous carbon microspheres (CoxP/NC) possess uniform distribution of graphite-encapsulated CoxP, a large surface area (826 m(2) g(-1)) and abundant mesopores. It was found the CoxP/NC exhibited excellent electrocatalytic performances toward 4-nitrophenol (4-NP). Therefore, CoxP/NC was developed to fabricate an ultrasensitive electrochemical sensor for 4-NP by using differential pulse voltammetry (DPV). In comparison with glassy carbon electrode (GCE) and nitrogen-doped carbon (NC) modified GCE, the CoxP/NC modified GCE (CoxP/NC/GCE) showed a remarkable increase in DPV current toward 4-NP. Under optimized condition, an ultrahigh sensitivity of 20.9 (mu A mol(-1) L) and a low detection limit of 2 x 10(-9) mol L-1 (at a signal-to-noise ratio of 3, S/N = 3) for 4-NP were achieved. Additionally, the CoxP/NC/GCE was successfully applied to detect 4-NP in tap water with good recoveries for its attractive selectivity and repeatability, which indicated that CoxP/NC could be a promising candidate for analyzing 4-NP.