Geldart Group C particles with the addition of nanoparticles (Group C+) show a better flowability and fluidization quality. The stability of these Group C+ particles with different nanoparticle concentrations were systematically examined in this work, including the flow properties, the particle size distribution (PSD), and the fluidization behaviors with the fluidizing time. Although the flowability, PSD, and fluidization behaviors for Group C+ particles fluctuated with the fluidizing time, those became more stable after fluidizing for 1-2 h. The increase of the nanoparticle concentration significantly improved the stability of these behaviors for Group C+ particles. Group A particles showed more stable behaviors with the fluidizing time than Group C+ particles, and nanoparticles had a little effect on the stability. In addition, Group C+ particles exhibited much better fluidization behaviors, including higher bed expansion and higher dense phase expansion, than Group A particles, contributing to better gas-solid contact. (C) 2021 Elsevier B.V. All rights reserved.