In this study, the micro gas sensor for NOx gas was fabricated by using a MEMS technology and sol-gel process. The sensing electrode and micro heater were designed to be a co-planar typed structure in the Pt thin film layer. The fabricated micro platform had a low power consumption of 67 mW at 2.0 V of heater voltage and 300°C of operating temperature. Indium oxide as a sensing material for NOx gas was synthesized by a sol-gel process with indium isopropoxide. The particle size of synthesized In2O3 was identified as about 50 nm. The maximum gas sensitivity as relative resistance (Rs = Rgas / Rair) occurred at 300°C with the value of 8.0 at 1 ppm NO2 gas. The present study shows that a MEMS-based gas sensor is a potential candidate for the automobile AQS (air quality system) gas sensor with many advantages of small dimension, high sensitivity, short response time and low power consumption.