OBJECTIVE： To prepare enteric-coated silymarin-PLGA nanoparticles， and to study its in vitro release behavior. METHODS： Using HPMCP as enteric-coated material， nanoprecipitation method was used to prepare enteric-coated silymarin-PLGA nanoparticles and silymarin-PLGA nanoparticles. The morphology of nanoparticles were observed， and the particle size， Zeta-potential， encapsulation efficiency， drug-loading amount， stability and in vitro release rate （Q） were detected. The ratio of PLGA-HPMCP in enteric-coated silymarin-PLGA nanoparticles was screened by using particle size， encapsulation ratio and drug-loading capacity as indexes. RESULTS： The best PLGA-HPMCP ratio was 1 ∶ 0.25. The particle size of enteric-coated silymarin-PLGA nanoparticles and silymarin-PLGA nanoparticles were 224 nm and 193 nm， Zeta potential were －37.8 mV and －40.7 mV； encapsulation ratio were （74.7±2.2）％ and （71.7±2.5）％， and drug-loading amount were （5.39±0.24）％ and （5.21±0.22）％； the percolation rates of them were 0.2％ and 0.5％ at 4 ℃ 3 months later； Q48 h of them in simulated gastric fluid were 38.6％ and 70.5％， and Q48 h of them in simulated intestinal fluid were 80.2％ and 73.5％， respectively. CONCLUSIONS： The enteric-coated silymarin-PLGA nanoparticles are prepared successfully with good stability， and can effectively inhibit the release of silymarin in simulated gastric fluid.