Vapor-phase catalytic reactions of several alcohols were investigated over In 2 O 3 . In 2 O 3 showed stable catalytic activity in the dehydration of terminal diols, such as 1,4-butanediols and 1,5-pentanediol, to produce unsaturated alcohols, such as 3-buten-1-ol and 4-penten-1-ol, respectively, with selectivities higher than 70 mol%. Although the dehydration of 1,3-diols, such as 1,3-propanediol and 1,3-butanediol, also proceeded over In 2 O 3 , the catalytic activity decreased with time on stream because of dehydrogenation followed by retro aldol reaction of the resulting dehydrogenated products. In contrast, in the reaction of monoalcohols, such as 1-butanol and 2-octanol, dehydrogenation dominantly proceeded to produce butanal and 2-octanone, respectively. Although In 2 O 3 has cubic bixbyite crystal structure that is the same as those of heavy rare earth oxides, the catalytic activity of In 2 O 3 was similar to that of cubic fluorite CeO 2 with redox property, rather than those of heavy rare earth oxides with acid-base property. Redox sites of In 2 O 3 are concluded to be active centers for the dehydration of diols to produce unsaturated alcohols.