Enhanced permeation and retention(EPR) targeting effect of rhodamine B labeled PEG-b-P(LA-co-DHP)[PEG:poly(ethylene glycol); LA:L-lactide; DHP:2,2-dihydroxylmethyl-propylene carbonate]micelles(RhBmicelles) was observed in H22 liver cancer bearing mice.The RhB-micelles were prepared by conjugating rhodamine B with the DHP units of amphiphilic block copolymer PEG-b-P(LA-co-DHP) followed by subsequent self-assembling of the conjugate.The parent copolymer PEG-b-P(LA-co-DHP) was synthesized by ring-opening copolymerization of LA and DHP with PEG as macroinitiator and diethyl zinc(ZnEt2) as catalyst.The micelles have a spherical shape and the average diameter is ca.50 nm by TEM(transmission electron microscope) or 80 nm by DLS(dynamic light scattering).Their in vitro cell uptake experiment by CLSM(confocal laser scanning microscopy)and flow cytometry showed preferential internalization of micelles by MCF-7 human breast cancer cells to free RhB.The in vivo tests by live animal imaging and ex vivo excised organ imaging showed that after vena tail injection,free RhB molecules were distributed in the whole body through the circulation system and then gradually metabolized and excreted and there was no preferential partition in tumor bed from the beginning to the end.But the RhB-micelles were preferentially distributed to the tumor bed so that their concentration(fluorescent intensity) in tumor bed got the level of the liver at a certain time point between 1 and 6 h and reached a maximum relative intensity at around 12 h,indicating an obvious EPR effect of RhB-micelles in H22 liver cancer.