Objective：To prepare stable, small-sized injectable sustained-release nanoparticles harboring brain-derived neurotrophic factor (BDNF) and to evaluate its drug releasing process.Methods: The nanoparticles were prepared using poly(D,L-lactic-co-glycolic acid) (PLGA) as the carrier by w/o/w double emulsion-solvent evaporation method.The formula and technique were optimized; the shape,size and the distribution of the diameters of the particles were observed; and recovery rate,precision,repeatability,encapsulation efficiency,and drug releasing characteristics were assessed.Results: With the optimized formula,the drug loading rate was 1%,the polymer concentration was 3.3 mg/ml, and the ultrasound time was 40 s; mannitol was used as the supporting agent.BDNF nanoparticles were round,homogenous in size,with a mean diameter of 156.7 nm.The prepared particles had high recovery rate,precision,repeatability,and encapsulation efficiency.The drug release was characterized by slow corrosion and the process lasted for 30 days.Conclusion: We have successfully prepared slow-release nanoparticles harboring BDNF,which are stable and have high encapsulation efficiency.