Third order nonlinear optical properties of symmetric alkylamino antraquinons were studied with three dimensional degenerate four wave mixing. The third order nonlinear optical susceptibilities |χ (3) | and the third order hyperpolarizabilities γ of 11 alkylamino anthraquinones in the solution of DMF were measured to be 1.8～3.4×10 -13 esu and 1.9～3.5×10 -31 esu respectively. The influence of the molecular structure upon the third order nonlinear properties of the materials was analyzed.