A porous formed body (Y) including a porous formed body (X) that satisfies the following (x-1) to (x-3), and an alkali metal carbonate or an alkali metal bicarbonate, in which a content of the alkali metal carbonate or the alkali metal bicarbonate is in a range of from 1 part by mass to 230 parts by mass, with respect to 100 parts by mass of the porous formed body (X), and a production method thereof, an α-olefin dimerization catalyst and a production method thereof, and a method of producing an α-olefin dimer:requirement (x-1): a volume of pores with a pore diameter in a range of from 0.01 µm to 100 µm is from 0.10 mL/g to 1.00 mL/g;requirement (x-2): a median pore diameter of pores with a pore diameter in a range of from 0.01 µm to 100 µm is from more than 0.01 µm to 10.0 µm; andrequirement (x-3): a crushing strength is from 0.7 kgf to 15.0 kgf.