A tumor-targeting antisense oligodeoxynucleotide (ODN) delivery system based on polyelectrolyte complex (PEC) micelles is demonstrated. ODN-PEG-folic acid (ODN-PEG-FA) was synthesized using a heterofunctional PEG linker. The PEC micelles for the targeted ODN delivery to tumor cells were produced by ionic interactions between the ODN-PEG-FA and polyethylenimine (PEI). The in vivo targeting properties of the PEC micelles were assessed using a mouse tumor model. The size of ODN-PEG-FA/PEI PEC micelles was 92.3 nm with a relatively narrow distribution. Cellular uptake of the ODN-PEG-FA/PEI PEC micelles by folic acid receptor over-expressing cells (KB) was greatly enhanced compared to that of ODN-PEG/PEI PEC micelles. When the ODN-PEG-FA/PEI PEC micelles were systemically administered to the mice bearing KB cell xenograft tumor, ODN was accumulated to the solid tumor in a target specific manner. This study suggests that the PEC micelles with a receptor-recognizable targeting ligand on the surface have potential for passive and active targeted delivery of ODN drugs to cancer cells.