Sima Lang 司馬朗 (171-217), courtesy name Boda 伯達, was an official of the warlord Cao Cao 曹操 in the last decades of the Eastern Han period 東漢 (25-220 CE).
He hailed from Wen 溫 in the commandery Henei 河內 (today's Wenxian 溫縣, Henan), was a son of Sima Fang 司馬防 and an older brother of Sima Yi 司馬懿. In the beginning he belonged as a *cadet gentleman (tongzilang 童子郎 ) to the retinue of the tyrant Dong Zhuo 董卓 who forced Emperor Xian 漢獻帝 (181-234, r. 189-220) to resettle in Chang’an 長安 (modern Xi'an 西安, Shaanxi) in the west. Guessing that Dong's time would be over, he more or less bought himself free, and returned to his hometown, where he engaged in scholarly studies, in spite of the famine affecting the region. Later on Cao Cao made him section manager under the Minister of Works (sikong yuan 司空掾).
Sima Lang then rose to the posts of magistrate (ling 令) of Chenggao 成皋, then of Yuancheng 元城. He then was made recorder of the Counsellor-in-chief (chengxiang zhubu 丞相主簿), a position allowing him to suggest the reintroduction of local militia and the traditional well-field system (jingtian zhi 井田制), but Cao Cao did not adopt such measures. Sima Lang was then promoted to regional inspector (cishi 刺史) of the province of Yanzhou 兖州, a duty which he fulfilled excellently. He died by a disease when participating in a campaign against the southeastern warlord Sun Quan 孫權, commanded by Xiahou Chun 夏侯惇 and Zang Ba 臧霸.