Four　kinds　of　ferrites,　MFe2O4　(M　=　Cu,　Zn,　Cd　and　Mg),　having　high　specific　surface　area　(40-80　m2/g)　were　prepared　by　a　coprecipitation　method　and　tested　for　sensing　properties　to　reducing　gases　of　CO,　H2,　LPG,　C2H5OH　and　C2H2.　The　gas　sensitivity　depended　considerably　on　the　kinds　of　ferrites　and　the　gases　to　be　detected.　All　of　the　ferrites　were　more　sensitive　to　C2H2,　C2H5OH　or　LPG　than　to　H2　or　CO.　Among　the　ferrites,　the　gas　sensitivity　tended　to　decrease　in　the　order　MgFe2O4　to　approximately　CdFe2O4>CuFe2O4>ZnFe2O4,　which　was　in　fact　coincident　with　the　increasing　(or　decreasing)　order　in　specific　surface　area　(or　grain　size).　It　was　revealed　that　MgFe2O4　and　CdFe2O4　were　the　most　sensitive　and　selective　to　LPG　and　C2H2,　respectively,　among　the　ferrites　tested.