Cd 1 - x Ag x In 2 O 4 (0.0=<x=<0.30) were synthesized with a chemical coprecipitation method. The phase constituents of Ag doped Cdln 2 O 4 materials were characterized by X-ray diffraction (XRD). Indirect-heating sensors were fabricated based on the materials. It is found that the Cd 0 . 9 0 Ag 0 . 1 0 In 2 O 4 -based sensor shows lower conductivity and exhibits higher sensitivity to reducing gases and shorter response times than CdIn 2 O 4 -based sensor.