Background As a monoamine neurotransmitter, 5‐hydroxytryptamine (5‐HT) or serotonin modulates mood, appetite, and sleep. Besides, 5‐HT also has important peripheral functions. 5‐HT receptor 2B (5‐HT2BR) plays a key role in cardiovascular diseases, such as pulmonary arterial hypertension and cardiac valve disease. Percutaneous intervention has been used to restore blood flow in occlusive vascular disease. However, restenosis remains a significant problem. Herein, we investigated the role of 5‐HT2BR in neointimal hyperplasia, a key pathological process in restenosis. Methods and Results The expression of 5‐HT2BR was upregulated in wire‐injured mouse femoral arteries. In addition, BW723C86, a selective 5‐HT2BR agonist, promoted the injury response during restenosis. 5‐HT and BW723C86 stimulated migration and proliferation of rat aortic smooth muscle cells. Conversely, LY272015, a selective antagonist, attenuated the 5‐HT–induced smooth muscle cell migration and proliferation. In vitro study showed that the promigratory effects of 5‐HT2BR were mediated through the activation of mammalian target of rapamycin (mTOR)/p70S6K signaling in a β‐arrestin2–dependent manner. Inhibition of mammalian target of rapamycin or p70S6K mitigated 5‐HT2BR–mediated smooth muscle cell migration. Mice with deficiency of 5‐HT2BR showed significantly reduced neointimal formation in wire‐injured arteries. Conclusions These results demonstrated that activation of 5‐HT2BR and β‐arrestin2–biased downstream signaling are key pathological processes in neointimal formation, and 5‐HT2BR may be a potential target for the therapeutic intervention of vascular restenosis.