Abstract: The present invention relates to a porous catalyst body for decomposing hydrocarbons, comprising a porous composite oxide comprising at least magnesium and/or calcium, and aluminum, and metallic nickel having a particle diameter of 1 to 25 nm, wherein the porous catalyst body has an average crushing strength of not less than 5 kgf and a displacement length of not less than 0.05 mm as measured by compressing the porous catalyst body under a load of 5 kgf. The porous catalyst body for decomposing hydrocarbons according to the present invention is less expensive, and has an excellent catalytic activity for decomposition and removal of hydrocarbons, an excellent anti-sulfur poisoning property, a high anti-coking property even under a low-steam condition, a crushing strength and a displacement length which are optimum for DSS operation, and an excellent durability.