La0.8Sr0.2Ga0.8Mg0.2O3 - delta (LSGM) and La0.8Sr0.2(Ga0.8Mg0.2)(1 - x)CrxO3 - delta (LSGMC, x = 0.1, 0.3, 0.5, 0.7 and 0.9) were prepared by high temperature solid-state reaction and their properties were characterized by X-ray diffraction, thermal expansion measurement and Van Der Pauw D.C. four-probe method. The properties of LSGM and LSGMC (x = 0.5, 0.7) make them well suited to act as oxygen sensor. A new type of limiting current oxygen sensor with LSGM solid electrolyte and LSGMC (x = 0.5, 0.7) dense diffusion barrier was fabricated. The sensor exhibits a good limiting current platform over a wide range of oxygen concentration from 1.92% to 21% at 1073-1123 K for x = 0.5, and 873-1123 K for x = 0.7. The limiting current is directly proportional to oxygen concentration. The sensors have high measurement accuracy. For the sensor with LSGMC (x = 0.7), the operating voltage ranges from 1.21 V to 1.34 V at 1073 K, and from 1.02 V to 1.34 V at 1123 K. The activity energy for electrical conductivity decreases with the increasing doping concentration. The activity energy for oxide-ion diffusion decreases slightly with the increasing oxygen concentration. The oxygen sensor based on perovskite structure LSGM and LSGMC (x = 0.5, 0.7) is expected to have a potential application.