EB1 (end-binding protein 1) is a key player in the regulation of microtubule dynamics. In concert with its binding partners, adenomatous polyposis coli and p150(glued), EB1 plays a crucial role in a variety of microtubule-based cellular processes. In this study we have identified in a yeast two-hybrid screen the mitotic kinase and chromosome passenger protein Aurora-B as a binding partner of EB1. GST pull-down and immunoprecipitation experiments reveal a specific interaction between Aurora-B and EB1 both in cells and in vitro. Immunofluorescence microscopy shows that these two proteins colocalize on the central spindle in anaphase and in the midbody during cytokinesis. Kinase assays using both immunoprecipitated and purified Aurora-B demonstrate that EB1 is not a substrate of Aurora-B. Rather, EB1 positively regulates Aurora-B kinase activity. EB1 overexpression remarkably enhances Aurora-B activity and knockdown of its expression impairs Aurora-B activity. Our data further show that EB1 is able to protect Aurora-B from dephosphorylation/inactivation by protein phosphatase 2A (PP2A) by blocking PP2A binding to Aurora-B. These findings establish Aurora-B as an EB1-interacting protein and suggest that EB1 stimulates Aurora-B activity through antagonizing its dephosphorylation/inactivation by PP2A.