Doxorubicin was chemically conjugated to a terminal end group of poly(D,L-lactic-co-glycolic acid) [PLGA] by an ester linkage and the doxorubicin-PLGA conjugate was formulated into nanoparticles. A carboxylic acid end group of PLGA was conjugated to a primary hydroxyl group of doxorubicin. The primary amine group of doxorubicin was protected during the conjugation process and then deprotected. The nanoparticles containing the conjugate exhibited sustained doxorubicin release profiles over a 1-month period, whereas those containing unconjugated free doxorubicin showed a rapid doxorubicin release within 5 days. Doxorubicin release patterns could be controlled by conjugating doxorubicin to PLGA having different molecular weights. The conjugated doxorubicin nanoparticles showed increased uptake within a HepG2 cell line, which was quantitated by a flow cytometry and visualized by confocal microscopy. The nanoparticles exhibited slightly lower IC(50) value against the HepG2 cell line compared to that of free doxorubicin. In vivo anti-tumor activity assay also showed that a single injection of the nanoparticles had comparable activity to that of free doxorubicin administered by daily injection. The conjugation approach of doxorubicin to PLGA was potentially useful for the formulation of nanoparticles that requires targeting for cancer cells as well as sustained release at the site.