Estrogen receptorβ (ERβ) plays an important role in the development and progression of cardiovascular disease, but the mechanism is not clear yet. Thus, it is of great significance to discover ERβ interacting coregulators. It was identified a non-receptor tyrosine kinase c-abl as a novel ERβ cofactor. Both GST pull-down and co-IP assay indicated that ERβ interacted with c-abl in vivo and in vitro, and phosphorylation immunoblotting showed that ERβ can be phosphorylated by c-abl. Furthermore, the luciferase assay showed that c-abl enhanced ERβ mediated transcriptional activities, while c-abl inhibitor STI571 abolished c-abl mediated upregulation of ERβ transcriptional activity. These data suggest that c-abl was a novel co-activator of ERβ, which may uncover a role of ERβ signaling in cardiovascular disease.