Abstract: Provided is a method for producing a propylene oligomer, which is advantageous in that a lowly branched propylene oligomer can be obtained at high selectivity. A method for producing a propylene oligomer, including an oligomerization step of oligomerizing propylene at lower than 160° C. in the presence of at least one member selected from a group consisting of a catalyst containing crystalline molecular sieve and a catalyst containing phosphoric acid, a fractional distillation step of obtaining a fraction containing a propylene trimer, a propylene tetramer, or a mixture thereof, and an isomerization step of isomerizing the propylene trimer, propylene tetramer, or mixture thereof contained in the fraction in the presence of a catalyst containing phosphoric acid.