Block copolymers have been used extensively in the synthesis of different types of nanoparticles. A novel ABA type tri-block nanopolymer PNIPAAm-b-PU-b-PNIPAAm has been synthesized via atom transfer radical polymerization (ATRP) technique, using a tertiary bromo-terminated as a macroinitiator. Herein, the triblock copolymer acts as both reducing and stabilizing agent. Gold-copolymer nanoparticles were synthesized in a green solvent using the tri-block copolymer and were well characterized by Transmission Electron Microscopy (TEM), Quassi Elastic Light Scattering (QELS) and UV-Vis. spectroscopy techniques. The shape and size of the obtained nanoparticles are dependent on the concentration ratio of copolymer/gold salt used in the synthesis. This study clearly indicates the average particles size of nanoparticles is ∼70 nm. The resultant gold-tri-block nanopolymer can be used in the fields of controlled release and delivery of drugs, nano-materials, medical devices etc.