Gas-involved sintering of supported nanoparticles is a common process of catalysts deactivation, but the mechanism is still ambiguous. Herein, we investigated the sintering behaviors of a Au-TiO2-(1 0 1) model catalyst in different gas environments via in situ environmental transmission electron microscopy (ETEM), spherical aberration (Cs-) corrected scanning transmission electron microscopy (STEM) and ex situ annealing experiments. Distinct sintering behaviors of Au-TiO2 catalysts were observed in ETEM that O-2 or O-2/CO mixed atmospheres facilitated but CO inhibited the sintering process. Ex situ annealing experiments were in accordance with in situ results. Further study with Cs-corrected STEM showed that TiO2 support annealed in CO got rougher and more defective than that annealed in O-2, which suppressed the free movement of Au particles on TiO2 surface. (C) 2020 Elsevier Inc. All rights reserved.