<p>To explore the effect of the rare earth element cerium (Ce) on the Co-8.8Al-9.8W alloy, this study investigates the microstructure, distribution of grain boundary characteristic, changes of grain size, element distribution, and existing forms of Ce in the Co-8.8Al-9.8W-<i>x</i>Ce (<i>x</i> = 0, 1, and 3 at.%) alloy using x-ray diffraction (XRD), scanning electron microscopy (SEM + EDS), transmission electron microscopy (TEM + EDS), and electron backscattering diffraction (EBSD). The findings demonstrate that the heat-treated alloys exhibit a typical γ-Coss/γ′-Co₃(Al, W) microstructure, with the largest γ′ phase volume percentage (88.2%) seen in the 1Ce alloy. In the base alloy Co-8.8Al-9.8W, the phase composition at the grain boundary is γ + Co₃W, whereas in the Ce-doped alloy, the primary phase is Co₇W₆, and the phase composition at the grain boundary is γ + Co₇W₆ + Co₃W. Ce also impacts the precipitation morphology of the Co₇W₆ phase. The distribution of grain boundaries in all the alloys is dominated by Σ3, and as the Ce content increases, the fraction of Σ3 grain boundaries decreases. In contrast, the 1Ce alloy has the highest proportion of low-angle grain boundaries and the most pronounced grain refinement effect. At the alloy grain boundary, Ce is slightly enhanced and serves as a purification agent.</p>