Abstract: OBJECTIVE To prepare methoxyl poly(ethylene glycol)-poly(lactic-co-glycolic acid)-hydroxy camptothecin nanoparticles(MePEG-PLGA-HCPT-NPs) by an improved dialysis method, and to characterize the nanoparticles. METHODS Using drug-loading and diameter as indexes, each single factor test was used to optimize the preparation technology. The appearance, diameter, Zeta potential, drug-loading and entrapment efficiency were investigated. RESULTS The optimal preparation conditions for MePEG-PLGA-HCPT-NPs were as follows: initial organic solvents was acetone; temperature was 25 ℃; initial water content was 1%; pH of external phase was 4.0; initial copolymer concentration was 3 mg·mL^-1; PEG content of copolymer was 15%; lactic acid content of copolymer was 100 %; the ratio of HCPT to MePEG-PLGA was 1∶5. Based on these experimental results, it was proposed that MePEG-PLGA-HCPT-NPs exhibited a solid spherical shape, fairly uniform size, well dispersed, and relatively smooth surface with core-shell structure. The average particle diameter was (120.1±2.4)nm, polydispersity was 0.057±0.021, Zeta potential was (-31.2±0.98)mV, the drug-loading was 7.42% and the entrapment efficiency respectively was 44.5%. CONCLUSION The improved dialysis method is suitable to prepare the MePEG-PLGA-HCPT-NPs, and it can lay a foundation for the future tests.