The evolution of size and shape of gold nanoparticles was studied during long-time aging. The initial particle size of 2-5 nm increased to about 25 nm in one year of storage. It was revealed that the main mechanism of particle growth is Ostwald ripening, however, fusion of particles was also observed. Additionally, while the initial particles have spherical morphology, the grown particles show various shapes such as sphere, bipyramid, decahedron, deca-tetrahedron, triangular plate and rod. Twin boundaries with large frequency of similar to 5% were detected inside the particles which have an important effect on the evolution of morphology. This study suggests that aging may be a new way of tuning size and shape of gold nanoparticles. (C) 2013 Elsevier B.V. All rights reserved.