Influence of La2O3 loading on the structural and gas sensing properties of SnO2 have been studied. The effect of different weight percentages of La2O3 (1-10 wt.%) in SnO2, and the effect of calcination temperature on the sensitivity to various reducing gases like LPG, H-2 and CH4 has been studied. The structural characteristics have been investigated by X-ray diffraction, and the corresponding crystallite size estimated. In addition to the systematic variation in the crystallite size as a function of the sintering temperature, the role of La2O3 as an effective grain growth inhibitor has been confirmed. Increasing the percentage of La2O3 above 2 wt.% has no added advantage in terms of improving the gas sensing characteristics and also in stabilizing the SnO2 surface. Once the La2Sn2O7 formation temperature is reached, the sensitivity of the sensor decreases marginally. At this temperature the crystallite size also increases very abruptly. All these have been correlated with the formation of the La2Sn2O7, a new phase with standard pyrochlore structure.