Esophageal cancer prognosis remains poor in current clinical practice. We previously reported that moscatilin can induce apoptosis and mitotic catastrophe in esophageal cancer cells, accompanied by upregulation of polo-like kinase 1 (Plk1) expression. We aimed to validate in vitro activity and Plk1 expression in vivo following moscatilin treatment and to examine the treatment’s radiosensitizing effect. Human esophageal cancer cells were implanted in nude mice. Moscatilin was intraperitoneally (i.p.) injected into the mice. Tumor size, body weight, white blood cell counts, and liver and renal function were measured. Aberrant mitosis and Plk1 expression were assessed. Colony formation was used to measure survival fraction after radiation. Moscatilin significantly suppressed tumor growth in mice bearing human esophageal xenografts without affecting body weight, white blood cell counts, or liver and renal function. Moscatilin also induced aberrant mitosis and apoptosis. Plk1 expression was markedly upregulated in vivo. Moreover, moscatilin pretreatment enhanced CE81T/VGH and BE3 cell radioresponse in vitro. Moscatilin may inhibit growth of human esophageal tumors and sensitize esophageal cancer cells to radiation therapy.