Higher molecular weight of the polymer carrier is the basis for enhanced accumulation of the pro-drug in a solid tumor tissue due to a tumor-related phenomenon described as the enhanced permeability and retention (EPR) effect. The anticancer drug doxorubicin was covalently bound to F127 through amide group susceptible to lysosomal hydrolysis. The in vitro and in vivo properties of F127-DOX amide conjugates were studied. F127-DOX amide conjugates (Mw: 13,400) were stable in neutral circumstance and showed the potency and mechanism of action of the released drug. In the in vivo experiment, results showed that F127-DOX amide conjugates prolonged blood circulation and lowered in vivo toxicity than corresponding DOX, which illustrated the importance of molecular weight. The results demonstrated that F127-DOX amide conjugates may be very promising and clinically suitable candidates for anticancer therapy. (c) 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2011