OBJECTIVE： To prepare Magnolol nano-crystal suspension （MAG-NS）， and to conduct quality evaluation. METHODS： The preparation technology of MAG-NS was optimized by central composite design-response surface methodology with OD value of particle size and polydispersity coefficient as evaluation indexes， using volume ratio of organic phase to water phase， ratio of excipient to drug， concentration of magnolol as factors and conduct validation tests. The quality of MAG-NS prepared optimal technology was evaluated. RESULTS： Optimized technology included that the volume ratio of organic phase to water phase was 1 ∶ 5， mass ratio of excipient to drug was 4 ∶ 1， concentration of magnolol was 2 mg/mL. In 3 times of validation tests， average OD value was 0.940 0 （RSD＝0.08％）， relative error of which to predicted value 0.977 7 was 3.86％. magnolol nano-crystals of MAG-NS prepared by the optimal technology were spherical， uniform in size， smooth in surface， with particle size of （34.88±0.33） nm， polydispersity coefficient of 0.032±0.001 and drug loading amount of （17.83±0.92）％. CONCLUSIONS： Established preparation method is simple and feasible. Prepared MAG-NS is in line with quality requirements. It can provide reference for further development and utilization of MAG-NS.