Abstract: Abstract Aim： To prepare vinblastine-loaded PCL-PEG₆₀₀₀-PCL nanoparticles，and to study their physicochemical properties and in vitro antitumor activity. Methods： PCL-PEG₆₀₀₀-PCL triblock copolymer was prepared by ring-opening polymerization，and vinblastine-loaded PCL-PEG₆₀₀₀-PCL nanoparticles was prepared by coprecipitation.The morphous，particle size，polydisperse index，particle yield，the drug-loading content，the encapsulation efficiency and in vitro release rate of these vinblastine-loaded nanoparticles were determined.The cytotoxicity of vinblastine-loaded nanoparticles to K562/A02 leukimia cell line was determined by MTT assay. Results： It was found using transmission electron microscopy(TEM) that the nanoparticles exhibited a spherical shape with core-shell structure.The particle sizes of the nanoparticles obtained by dynamic light scattering were (185±2.7) nm.The drug loading content and the encapsulation efficiency were determined to be 28.83% and 86.52%，respectively. in vitro release study revealed that more than 70% of accumulative release of entrapped vinblastine was reached in 9 hr and that nearly complete release was achieved in 24 hr.The inhibition of vinblastine-loaded nanoparticles to K562/A02 cell line was significantly increased as compared with that of the same dose of sulfate vinblastine solution. Conclusions： PCL-PEG-PCL nanoparticles could be used as a carrier of vinblastine，and the prepared nanoparticles exhibited a spherical shape，high encapsulation efficiency，relevant stablity and sustained-release properties.The cytotoxicity of vinblastine to K562/A02 cell line was significantly increased when it was encapsulated in PCL-PEG-PCL nanoparticles.