The synthesis and characterization of organic nanoparticles composed of a polymer network of azobenzene moieties and capable of reproducible, photoinduced mechanical actuation are reported. The molecules within the nanoparticles undergo co-ordinated, reversible isomerization between cis- and trans-conformations in response to ultraviolet and visible electromagnetic radiation, resulting in a reversible 20% height contraction of nanoparticles adsorbed on a substrate. The kinetics of the actuation response as a function of light intensity and duration are reported and closely match the molecular kinetics of azobenzene photoisomerization. The results support the proposed mechanism of co-ordinated molecular conformational changes resulting in observable nanoscale actuation. The synthesis and characterization of an opto-responsive nanoparticle capable of reversible shape change is described. Co-ordinated photoisomerization of azobenzene molecules imparts a conformational change to the polymer network of the nanoparticle and results in a measurable and reproducible shape change. Copyright © 2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.