PURPOSE: To obtain a 1-butene at a high selectivity and high dimerization rate by using a catalyst system consisting of a compd., such as Pd compd. anion-2- pyridyldiphenyl phosphine of a specific acid.

CONSTITUTION: At the time of obtaining the 1-butene by bringing ethylene into contact with the catalyst system in a nonprotonic solvent, the catalyst system consisting of (a) the palladium compd. (e.g.: palladium acetate, etc.), (b) the anion (e.g.; trifluoromethanesulfonic acid, etc.; and more adequately copper (II) salt) of the acid (excluding hydrohalic acid) of ≤2 in pKa measured at 18°C in an aq. soln. and (c) the compd. (e.g.; 2-cyanoethyldiphenyulphosphine, etc.), which contains at least one phosphorus and ≥1 n not having H and in which each N is bonded to P by an org. bridge group contg. at least one C within the bridge bond is used.