The microencapsulation method was used to prepare formulations of the anthracycline drug aclarubicin, and the effects of a variety of different conditions on the preparation process were evaluated. The drug was entrapped in poly(lactic-co-glycolic acid) (PLGA) to prepare an aclarubicin nanosphere formulation that could be sustainably released, and had a high drug loading capacity and high entrapment efficiency. The degree of degradation of aclarubicin PLGA nanospheres that were prepared under different conditions was tested in vitro. Aclarubicin nanospheres that were intravenously injected into rabbits were found to be slowly and stably released over a period of almost 20 days. HPLC was used to determine the blood concentrations of the products. To provide pharmacodynamic and toxicologic profiles, the aclarubicin PLGA nanospheres were intravenously injected into mice. The results showed that the aclarubicin PLGA nanospheres exerted anti-tumor activity in vivo, but did not produce toxic effects that were more serious than those resulting from the standard administration of aclarubicin agents. (C) 2010 Wiley Periodicals, Inc. J Appl Polym Sci 117: 2754-2761, 2010