A method for producing an α-olefin oligomer, the method including subjecting α-olefin to oligomerization reaction to produce an α-olefin oligomer mixture, carrying out distillation separation of α-olefin oligomer having less than n carbon atoms in the mixture to obtain a distillation residue containing α-olefin oligomer having n or more carbon atoms, and then carrying out a step of removing high molecular weight molecules from the distillation residue.