A new type of amperometric oxygen sensor was developed by an approach of co-pressing and co-sintering YSZ solid electrolyte. A dense LSM+YSZ composite electrode which was used as both cathode and diffusion barrier. Pre-sintered composite and YSZ powders were dry-pressed together to form a sheet with dual-layer of LSM+YSZ/YSZ. The sheet was then sintered at 1450°C. The anode was made of Pt paste, which was printed on to the other side of YSZ. The experiment results showed that the oxygen sensor exhibited a quite low operating temperature. At 400°C, the limiting current appeared in the voltage from 0.7 to 1.2V and the limiting current was a good linear relationship with the oxygen concentration up to 10 %. The sensor has some excellent features such as a rapid response, no reference gas, simple configuration and low cost. Taken together with the chemical stability of the diffusion barrier, the sensor is suitable for the control of air-to-fuel ratio in lean-burn internal combustion engines.