Metal carbides (MCs) serve as essential strengthening phases in nickel-based superalloys, so the decomposition of MCs during high-temperature creep is regarded as detrimental to the mechanical properties and service life of these alloys. However, detailed investigations of the MC decomposition process at the microscale remain limited. In this study, the microstructure of MCs (where M is a mixture of Ti and Ta) in a nickel-based superalloy was characterized using aberration-corrected scanning transmission electron microscopy. The MCs exhibit a spherical core–shell structure, with Ta enrichment in the shell and Ti segregation in the core. Moreover, a high density of Cr-rich stacking faults, accompanied by Cr-rich M₂₃C₆ precipitates at their terminations, was identified in the Ti-rich cores, suggesting that these defects may be closely associated with the decomposition of MCs. This study may further expand the fundamental understanding of the interactions between defects and carbide properties.