We report here the loading of the antitumor drug doxorubicin (DOX) in preformed multilayer microcapsules and its application in tumor treatment assayed by in vitro cell culture and in vivo animal experiments. The microcapsules, consisting completely of polysaccharides, were fabricated by deposition of oppositely charged chitosan and alginate onto carboxylmethyl cellulose (CMC)-doped CaCO(3) colloidal particles in a layer-by-layer fashion, followed by cross-linking with glutaraldehyde and decomposition of the cores by disodium ethylenediaminetetraacetic acid. The microcapsules as prepared contain negatively charged CMC-either in a free state or very possibly coupled with the excess chitosan of the first layer. They showed a strong ability to accumulate the positively charged DOX with a factor of tens to hundreds; that is, the drug concentration within the microcapsules was hundreds of times higher than the feeding concentration. Confocal microscopy and transmission electron microscopy revealed homogeneous distribution of the drug. The encapsulated DOX could be released again, following a diffusion-controlled model at the initial stage. In vitro experiments showed that the encapsulated drug can effectively induce the apoptosis of HepG2 tumor cells, as shown by various microscopy techniques after acridine orange, Hoechst 33342, and osmium tetraoxide staining. By seeding the HepG2 hepatoma cells into BALB/c/nu mice, tumors were created for the experimental studies. The results showed that the encapsulated DOX had better efficacy than that of the free drug in terms of tumor inhibition in a 4-week in vivo culture period.