The invention provides a catalyst for thermal decomposition of an organic substance having the form of spherical granule having a particle diameter of 0.1 to 1.2 mm, a pore volume of 0.1 to 0.3 mL/g, a tap density of 1.05 to 1.4 g/mL, and a wear rate of 2% by weight or less, the catalyst being obtained by mixing and granulating a pulverized product of an inorganic oxide exemplified by titanium oxide with at least one sol selected from a titania sol, a silica sol, an alumina sol, and a zirconia sol to make spherical granules, calcining the spherical granules at a temperature from 400 to 850° C., and sieving the calcined granules.