BACKGROUND: Phosphorylcholine-containing poly (L-lactide) (PLLA-PC) is a kind of novel amphiphilic copolymer with good biocompatibility and biodegradability. In the previous work, self-assembly micelles of PLLA-PC were prepared with film rehydration method. But it hardly formed micelle with film rehydretion method because the longer chains of LLA existed in the PLLA-PC copolymer. However, the mechanism of phosphotipid choline polymer with long hydrophobic chain forming micelle remains still unclear. OBJECTIVE: To prepare self-assembling nanoparticles of PLLA-PC using solvent evaporation method, and to explore the factors that affected the properties and stability of nanoparticles.METHOD: ① Nanoparticles were prepared with solvent evporation metod.PLLA-PC copolymer was dissolved into acetone, and the copolymer solution was added dropwise to distilled water with stirring to yield nanoparticles. The critical micelle concentration (CMC) was performed on the F-7000FL220-240V. The emission and excitation wavelength were 395 nm and 300 mm, respectively. Transmission electron microscopy (TEM) was carried out on a JEM-100CX electron microscope to observe the morphology of PLLA-PC nanoparticles. Dynamic light scattering measurements on nanoparticle solutions were performed on a NANOSIZE 3600 at room temperatire. ②Gel permeation chromatography(GPC)measurements were perfrmed on a Waters 717 apparatus equipped with an RI detector. THF was used as the mobile phase at a flow rate of 1.0 mlJmin. A 1 g/L solution (50 μL) was injected for each analysis. RESULTS AND CONCLUSION: TEM indicated that the PLLA-PC nanoparticles presented typical shell/core structure. The critical micelle concentration was determined by fluorescent probe method. The results showed that the CMCs were quite low ( 10~(-3) g/L) and were dependent on the LLA units in the copolymer. The size and size distribution of the nanoparticles were detected by dynamic light scattering. The results indicated that the size could be affected by the LLA units, concentration of the organic solution and the concentration of the aqueous solution of the nanoparticles. On the other hand, they hardly changed over the dilution with water, which was of great importance in venous injection. They degraded at 37℃. PLLA-PC nanoparticles with controllable sizes can be prepared with phase separation method and might serve as a novel material for drug delivery.