To provide a method for producing an olefin oligomer, with duration over a long period, in good yield and with good efficiency.

The production method for an olefin oligomer is carried out by making an olefin contact with a catalyst of an organopolysiloxane having a hydrocarbon group containing a sulfonic acid group, wherein the pore volume of the mesoporous part having 20-500 pore diameter accounts for 0-20% of the pore volume of the pores having 9-500 pore diameter.