Over the past decades, there has been increasing interest in developing a smart targeted cancer therapy to deliver chemotherapeutic drugs directly to cancer cells while minimizing the killing of healthy noncancerous cells. The success of such development lies in the design of nanoparticles that are capable of being taken up by the targeted cancer cells and release their drug payload intracellularly over an extended period to achieve a clinical response. In this study, we developed drug encapsulated nanoparticles that can be specifically taken up by the prostate cancer cells and release their encapsulated TaxotereŽ drugs over an extended period in vitro. The targeted nanoparticles were developed using an amphiphilic block copolymer containing the following three segments 1) a targeting molecule made of a ribonucleic acid (RNA) aptamer that can bind specifically to the human prostate cancer cells, 2) a segment of poly(ethylene glycol) (PEG) to maximize the nanoparticle circulation half life, 3) a segment of poly(D,L-lactide-co-glycolide) (PLGA) for encapsulation and sustained release of chemotherapeutic drugs. By systemically optimizing the nanoparticle composition, we identified the parameters that are important to achieve sustained drug release while maintaining efficient cancer targeting capability. Both in vitro cell binding and docetaxel release results demonstrated cancer cell specific targeting with sustained docetaxel drug release using the aptamer-PEG-PLGA triblock nanoparticles. The formulation of such polymer can be further developed as a platform technology for cancer therapeutic and diagnostic applications.