The influence of Se doping on the operating characteristics of In 2 O 3 -based gas sensors was studied. Here, In 2 O 3 -based ceramic beads were prepared by sol–gel technology. The Se concentration in the solution used for the synthesis of In 2 O 3 powders was varied in the range 0–10wt.%. O 3 (∼1ppm), CO (2000ppm) and H 2 (1000ppm) were used as the test gases. The addition of selenium into the In 2 O 3 matrix was found to be effective in increasing sensor response to the oxidizing gas, ozone. It was posited that this improvement is connected to optimization of the In 2 O 3 ceramic structure.