Abstract: Gambogic acid (GA), the main active ingredient in gamboge, has been reported to have good anti-tumor activity with excellent selectivity. However, its clinical application is limited by the poor water solubility. GA nanosuspensions were designed in this study in order to solve this problem. GA nanosuspensions were prepared by microprecipitation method based on pH adjustment. Suitable stabilizer was screened according to the size and polydispersity index (PDI) of the resultant nanosuspensions. Dynamic light scattering method was used to measure the particle size and transmission electron microscopy was used to observe the morphology. The stability was studied in different medium. The drug release was evaluated using a dialysis method. MTT assay was used to assess their cytotoxicity in vitro against cancer cell line. Anti-tumor effect in vivo was investigated on H22-bearing mice. In result, Poloxamer (P188) was found to be a good stabilizer. The resultant GA nanosuspensions (GA-NSps) were 135.9 ±5.1 nm in diameter, with PDI value being 0.26 ±0.01 and the zeta potential being −35.1 ±1.36) mV. GA-NSps were nearly spherical. They were quite stable in various physiological media. GA-NSps exhibited a sustained drug release pattern, with the cumulative release reaching 90.26% within 312 h. In MTT assay, GA-NSps had a stronger cytotoxicity against HepG2 cells than the free drug (IC₅₀, 0.851 8 μg·mL⁻¹ vs 2.104 μg·mL⁻¹, P < 0.05). The pharmacodynamics study suggest that the antitumor effect of GA-NSps was dose-dependent. The anti-tumor effect at the high dose is better than that of paclitaxel (72.35% vs 66.80%, P < 0.01). In summary, we prepared GA-NSps with high drug loading capacity, small particle size and good stability, and provided a solid basis for the effective dosage form of gambogic acid.