A novel electrochemical sensor for the determination of p-nitrophenol (PNP) was fabricated with the nanoscaled composite oxide Mg(Ni)FeO-modified carbon paste electrode (CPE), and its electrocatalytic performances were investigated using the cyclic voltammogram and differential pulse voltammetry techniques. The influential factors were optimized such as the mass ratio of Mg(Ni)FeO to graphite, the pH value of buffer solution and the accumulation time at open circuit. The indirect oxidation peak current of PNP was found to be proportional to its concentration between 2.0 x 10(-6) and 2.0 x 10(-4) M on the proposed sensor Mg(Ni)FeO/CPE under the optimal condition (10 % Mg(Ni)FeO/graphite, pH 5.0 HAc-NaAc, 120 s quiescence). The sensor Mg(Ni)FeO/CPE exhibited a high sensitivity of 811 mu A mM(-1) cm(-2) and a low detection limit of 0.2 mu Ie (S/N- = 3) for PNP detection, and got satisfactory results when it was applied to determine PNP in real samples. The results demonstrate that Mg(Ni)FeO/CPE based on the nanomaterial Mg(Ni)FeO with high specific area and mesoporous structure could be employed as an electrochemical sensor for PNP determination with simplicity, low cost, good selectivity, repeatability, and stability.