OBJECTIVE：To study the sta bility，in vivo release characteristics and tissue distribution of docetaxel （DTX）- dihydroartemisinin（DHA）conjugated prodrug self-assembled nanoparticles （DTX-S-S-DHA NPs ）. METHODS ：HPLC method was adopted to analyze DTX-S-S-DHA in vitro . The phycial and long-term stability of DTX-S-S-DHA NPs in mediums [water ， saline，phosphate buffer （PBS，pH 7.4）and RPMI 1640 medium] were investigated by using particle size ，polydispersity index （PDI）and encapsulation efficiency （EE）as evaluation indexes. The in vitro release characteristics of DTX-S-S-DHA released from DTX-S-S-DHA NPs was also investigated with small glass method ，using 30％ ethanol solution with or without 10 mmol/L dithiothreitol（DTT）as medium. The small live animal imager was adopted to investigate the tissue distribution and tumor targeting capability of DiR-labeled DTX-S-S-DHA NPs （DTX-S-S-DHA/DiR NPs ）in breast cancer bearing mice. RESULTS ：In stability test，there was no statistical difference in particle size ，PDI and EE of DTX-S-S-DHA NPs incubated in water ，normal saline ，PBS and RPMI 1640 medium for 24 h. When stored at 4 ℃，with the increase of storage time ，the particle size of DTX-S-S-DHA NPs in normal saline gradually increased ，while those in PBS gradually decreased ；EE of both gradually decreased to less than 75％， but there was no significant change in particle size ，PDI and EE of DTX-S-S-DHA NPs in water and RPMI 1640 medium. In the in vitro release experiments ，DTX-S-S-DHA in DTX-S-S-DHA NPs was not released in the release medium containing 10 mmol/L DTT；at 24 h，the cumulative release rate of DTX-S-S-DHA released from DTX-S-S-DHA NPs in release medium without DTT was about 83％，which was in line with first-order kinetic model. In tissue distribution test ，the distribution of DTX-S-S-DHA/DiR NPs in tumor sites of mice was significantly more than in other tissues （heart，liver，spleen，lung and kidney ）. CONCLUSIONS ： DTX-S-S-DHA NPs show good physical stability in different mediums ，especially have good long-term stability in water and RPMI ； 1640 medium；they can quickly release the parent drug in the reduction environment and has good tumor targeting.