The interface between metal catalyst and support plays a critical role in heterogeneous catalysis. An epitaxial interface is generally considered to be rigid, and tuning its intrinsic microstructure with atomic precision during catalytic reactions is challenging. Using aberration-corrected environmental transmission electron microscopy, we studied the interface between gold (Au) and a titanium dioxide (Ti[O.sub.2]) support. Direct atomic-scale observations showed an unexpected dependence of the atomic structure of the Au-TiC 2 interface with the epitaxial rotation of gold nanoparticles on a Ti[O.sub.2] surface during carbon monoxide (CO) oxidation. Taking advantage of the reversible and controllable rotation, we achieved in situ manipulation of the active Au-Ti[O.sub.2] interface by changing gas and temperature. This result suggests that real-time design of the catalytic interface in operating conditions may be possible.