Highly uniform NiO nano-particles with a crystallite size of about 3nm were obtained by room-temperature ball-milling of the parent Ni(OH) 2 , which was derived using a sol–gel method. The obtained nano-structured NiO precursor was then utilized for the fabrication of NiO-sensing electrodes (SEs), which were further examined in the mixed-potential-type YSZ-based planar NO 2 sensor. The obtained results revealed the attractive advantages for the application of mechanochemical approach in regard to achieve high NO 2 sensitivity, NO 2 selectivity and reproducibility. All of the evaluated sensors attached with the nano-structured NiO-SEs, regardless of its sintering temperature, were found to exhibit high NO 2 sensitivity at 800°C under the wet condition (5vol.% water vapor). In addition to high NO 2 sensitivity, the sensor attached with 1100°C-sintered NiO-SE showed highly selective properties towards NO 2 . The observed improvement in NO 2 -sensing characteristics as well as the attainment of highly reproducible behavior for different sensor devices is discussed based on morphological and electrochemical observations of the studied sensors.