Four　mixed　oxides　MFe2O4　(M　=　Cu2+,　Zn2+,　Cd2+　and　M2+)　have　been　prepared　and　characterized　by　means　of　powder　X-ray　diffraction　analysis　(XRD),　transmission　electron　microscope　(TEM)　and　specific　surface　area　measurement.　The　results　reveal　that　all　these　samples　are　spinel-type　mixed　oxide　nanopowders　with　high　specific　surface　areas　(40-80　m(2)/g).　The　gas　sensitivity　of　these　samples　to　reducing　gases,　such　as　liquefied　petroleum　gas　(LPG),　C2H2,　alcohol,　CO　and　H-2　has　been　determined.　It　is　found　that　there　are　certain　relationships　among　the　specific　surface　area,　grain　size,　XRD　peak　width　and　gas　sensitivity.　The　larger　specific　surface　area　and　smaller　grain　size　the　sample　has,　the　lower　crystallinity　and　larger　sensitivity　it　possesses.　Thus　the　grain　size　of　the　samples　increases　in　the　order　CdFe2O4CuFe2O4＞　ZnFe2O4.