Mixed-potential type (MPT) NO2 sensors equipped with CeO2-B2O3 (B = Fe, Cr) sensing electrode (SE) and yttria-stabilized-zirconia (YSZ-8Y) electrolyte are fabricated. The new ceria-based nanocomposites synthesized by sol-gel method improve the NO2 gas sensing properties significantly. The highest response to NO2 is found for the sensor using CeO2-Cr2O3 binary oxides with 1:1 Ce/Cr sintered at 800 °C, resulting in 100 mV to 100 ppm with relatively fast response and recovery times at the working temperature of 450 °C. A linear relation is obtained for the sensor with configuration of Pt/YSZ/CeO2-B2O3 (B = Fe, Cr) between potential difference (ΔV) and the logarithm of the concentration of NO2 from 5 to 200 ppm, which the sensitivities are 40.5 and 74.0 mV/decade, respectively. Additionally, the sensor’s reproducibility, selectivity, cross-sensitivity and stability are investigated in details. Furthermore, the mixed potential sensing mechanism and catalytic activity to NO2 for ceria-based nanocomposites are also discussed.