14–3–3 proteins are involved in several cellular processes, including the G1/S and G2/M cell cycle transitions. However, their roles during mitosis are not well understood. Here, we showed that depletion of 14–3–3η, a 14–3–3 protein isoform, enhanced mitotic cell death, resulting in sensitization to microtubule inhibitors and inhibition of aneuploidy formation. The enhanced mitotic cell death by depletion of 14–3–3η appeared to be both caspase-dependent and independent. Furthermore, enhanced mitotic cell death and a reduction in aneuploidy following 14–3–3η depletion were independent of the mitotic checkpoint, which is thought to be the primary signaling event in the regulation of the cell death induced by microtubule inhibitors. When 14–3–3η depletion was combined with microtubule inhibitors in HCT116 and U87MG cells, it sensitized both cancer cell lines to microtubule inhibitors. These results collectively suggest that 14–3–3η may be required for mitotic progression and may be considered as a novel anti-cancer strategy in combination with microtubule inhibitors.