This paper is concerned with a gas sensor composed of semi-conducting ${gamma}$-$Fe_2O_3$ ceramics made by oxidizing $Fe_2O_3$ sintered body. Acicular $alpha$-FeOOH powder prepared by precipitation of $FeSO_4$.$7H_2O$ solution was transformed to $FeSO_4$ sintered at 700$^{circ}$-850$^{circ}$C for 1 hr. and then oxidized to ${gamma}$-$Fe_2O_3$ The gas sensitive properties of ${gamma}$-$Fe_2O_3$ ceramic bodies based on the lectrical resistance change was measured in 0.5-2 vol% $H_2$ and $C_2$ $H_2$ gas at 35$0^{circ}C$ The specific surface area of sintered specimen largely dependent on the sintering temperature and grain shape directly affected the gas sensitive pro-perties of ${gamma}$-$Fe_2O_3$gas sensor. Specimens having larger specific surface area showed better sensitivity which means the electrical resistance change due to oxidation and reduction process occurs on ly at the surface of grains microscopically in the ${gamma}$-$Fe_2O_3$ceramics. Micropores made in $Fe_2O_3$ powder during dehydration of $alpha$-FeOOH can not prompt the gas sensitive properties of sintered ${gamma}$-$Fe_2O_3$ because they are sintered or closed in the grains during sintering process and dose not affect the specific surface area of sintered body.