Xian Zhen 先軫 (died 627 BCE) was a nobleman in the state of Jin 晉 during the Spring and Autumn period 春秋 (770-5th cent. BCE). Because his fief was called Yuan 原 (near modern Jiyuan 南濟, Henan), he is also known as Yuan Zhen 原軫. He was a member of the noble house of Xian 先 and served the dukes Wen 晉文公 (r. 637-628) and Xiang 晉襄公 (r. 628-621) as a general.
Xian Zhen's career began as assistant commander of the Lower Army (xiajun zuo 下軍佐), yet later he rose to the office of marshal of the Central Army (zhongjun yuanshuai 中軍元帥), a position similar to that of Counsellor-in-chief. During the battle of Chengpu 城濮 (near modern Zhencheng 鄄城, Shandong) he heavily defeated the army of Chu 楚.
When Duke Xiang succeeded to the throne the duke of Qin 秦 waged war against the state of Zheng 鄭. Xian Zhen suggested attacking Qin at the strategic point of Mt. Yao 殽山 (near modern Ningluo 寧洛, Henan). Jin obtained victory and captured the generals Baili Xi 百里奚 (Meng Mingshi 孟明視), Xi Qishu 西乞術 and Bai Yibing 白乙丙.
Yet Lady Wen Ying 文贏, a consort of Duke Wen who was a princess from Qin, suggested sending them home to be executed as a punishment for their failure. Xian Zhen was not very content about this amnesty. He died (probably intentionally) shortly later in a campaign against the Di tribes 狄. He was succeeded in office by his son Xian Qieju 先且居.