Abstract: OBJECTIVE To establish the process of preparation and the quality evaluation method of thethymopentin microspheres (TP-5). METHODS TP-5 loaded microspheres were prepared with poly (lactic-co-glyeolic acid) (PLGA) as carrier material by double emulsion(w/o/w)，to investigate the size, outside appearance and drug entrapment efficiency of the microspheres. HPLC method was used to determine the content of the TP-5 microspheres. RESULTS Microspheres with good shape were prepared by this method．The drug entrapment efficiency was more than 80%. Mean particle size was 67.8 mm. Under the release condition in vitro, cumulative drug release of microspheres was above 80% within 27 d. CONCLUSION The process of preparation of TP-5 microspheres is reasonable．The evaluation method is simple，rapid，accurate and suitable for the quality control of TP-5 microspheres.