Gas-sensing properties to dilute Cl-2 have been investigated for CdIn2O4 thick film sensors prepared by coprecipitation method. Cadmium nitrate and indium nitrate were mixed in de-ionized water. The 0.1 M NaOH was added to the mixed solution. The co-precipitate obtained was washed, filtered, dried, and calcined at 600-900 degreesC for 4 h. The CdIn2O4 sensor prepared using the powder calcined at 600 degreesC showed high sensitivity (S = R-g/R-a) to dilute Cl-2, at 250 degreesC. In particular, the CdIn2O4 sensor showed the sensitivity as high as 1200 even to 0.2 PPM Cl-2. The crystal structure and surface morphology were examined by means of X-ray diffraction (XRD) and scanning electron microscopy (SEM), respectively. (C) 2003 Published by Elsevier Ltd.