New pH-responsive polymersomes for active anticancer oligonucleotide delivery were prepared from triblock copolymers. The delivery systems were formed by two terminal hydrophilic blocks, PEG and polyglycerolmethacrylate (poly-GMA), and a central weakly basic block, polyimidazole-hexyl methacrylate (poly-ImHeMA), which can complex with oligonucleotides and control vesicle formation/disassembly via pH variations. Targeted polymersomes were prepared by mixing folate-derivatized and underivatized copolymers. At pH 5, ds-DNA was found to complex with the pH-responsive copolymers at a N/P molar ratio above ∼2:1, which assisted the encapsulation of ds-DNA in the polymersomes, while low association was observed at pH 7.4. Cytotoxicity studies performed on folate receptor overexpressing KB and B16-F10 cells and low folate receptor expressing MCF-7 cells showed high tolerance of the polymersomes at up to 3 mg/mL concentration. Studies performed with red blood cells showed that at pH 5.0 the polymersomes have endosomolytic properties. Cytofluorimetric studies showed a 5.5-fold higher uptake of ds-DNA loaded folate-functional polymersomes in KB cells compared to nontargeted polymersomes. In addition, ds-DNA was found to be localized both in the nucleus and in the cytosol. The incubation of luciferase transfected B16-F10 cells with targeted polymersomes loaded with luciferase and Hsp90 expression silencing siRNAs yielded 31 and 23% knockdown in target protein expression, respectively.