In-Sn co-doped ZnO nanoparticles were synthesized by simple combustion method. Different aging time was used for this synthesis process and it has been found that 24 h aging time is an ideal aging time. ZnO nanoparticles for 24 h aging time exhibiting complete photodegradation of DR-31 dye under UV irradiation. Photocatalytic activities for all the samples were observed in 120 min. Gas sensing property towards ethanol gas has been studied.