Secondary gamma' precipitation in a commercial single crystal Ni-based superalloy after the 1100 degrees C isothermal aging has been investigated by atom probe tomography. After the isothermal aging for 300 s, 1800 s and 3600 s, a bimodal size distribution of larger primary gamma' precipitates and numerous smaller secondary gamma' precipitates was obtained. It is proposed that the secondary gamma' precipitated via a non-classical nucleation mode. The coarsening of secondary gamma' precipitates well obeys the classical LSW theory. (C) 2014 Elsevier B.V. All rights reserved.