A method for producing an olefin dimer, including a step of subjecting an olefin containing an olefin having from 4 to 10 carbon atoms to a dimerization reaction in the presence of an olefin dimerization catalyst containing a compound (B) represented by B.sub.nX (wherein B is Na or K, X is CO.sub.3, SO.sub.4, SiO.sub.3, F, Cl, or Br, and n is an integer of 1 or 2 determined by a valence of X), and an alkali metal (D), a content ratio of which is in a specific range, and an olefin dimerization catalyst in which a pore diameter and a volume of pores of the compound (B) are within specific ranges.