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To minimize the systemic toxicity prevalent to chemotherapeutics, we designed a novel anticancer drug-encapsulating liposome conjugated with an RNA aptamer specific to the prostate specific membrane antigen (PSMA), which is expressed on the surface of prostate cancer cells. The RNA aptamer-conjugated liposome, termed an aptamosome, was prepared by the post-insertion method, in which RNA aptamer-conjugated micelles were inserted into a liposome. These nanosized (90–100 nm) aptamer-conjugated liposomes specifically bind to LNCaP prostate epithelial cells that express PSMA and thus cause the nanoparticles to have significantly enhanced in vitro cellular binding and uptake as compared with nontargeted nanoparticles that lack the PSMA aptamer. Aptamosomes encapsulated with the anticancer drug doxorubicin (Dox) were significantly more toxic to the targeted LNCaP cells than to nontargeted cancer cells. Dox-encapsulating aptamosomes administered to LNCaP xenograft nude mice were selectively retained in tumor tissue. We also demonstrated in vivo anticancer efficacy of the Dox-encapsulating PSMA-aptamosomes on tumor size regression in LNCaP xenograft mice. We suggest that the encapsulation of toxic chemicals with aptamer-conjugated liposomes will enable the use of these bioconjugates in clinical practice with fewer side effects.