李善兰（1810年－1882年）字壬叔，号秋纫，中国清朝数学家。浙江省杭州府海宁县人。为中国近代数学的前驱，清代数学史上的杰出代表。

李善兰于清嘉庆十五年（1810年）1月2日生于浙江海宁县硖石镇。10岁即通《九章算术》，15岁通习《几何原本》六卷，17岁参加杭州乡试未中。道光二十五年（1845年）以所着《四元解》二卷呈浙江名士顾观光，说“深思七昼夜，尽通其法”。从此钻研天文、历算，成为远近闻名的数学家。

1852年－1866年受聘于墨海书馆任编译。同治二年（1863年）被招至曾国藩幕中。同治五年（1866年）曾国藩出资三百金为李善兰刻《几何原本》后九卷。1868年，入同文馆总教习，执教算法，前后八年。同治十三年（1874年）升户部主事。光绪二年（1876年）升员外郎。光绪八年（1882年）升郎中。

Li Shanlan (李善兰, courtesy name: Renshu 壬叔, art name: Qiuren 秋纫) (1810 – 1882) was a Chinese mathematician of the Qing Dynasty.

A native of Haining, Zhejiang, he was fascinated by mathematics since childhood, beginning with the Nine Chapters on the Mathematical Art. He eked out a living by being a private tutor for some years before fleeing to Shanghai in 1852 to evade the Taiping Rebellion. There he collaborated with Alexander Wylie, Joseph Edkins and others to translate many Western mathematical works into Chinese, including Elements of Analytical Geometry and of the Differential and Integral Calculus by Elias Loomis, Augustus De Morgan's Elements of Algebra, and the last nine volumes of Euclid's Elements (from Henry Billingsley's edition), the first six volumes of which having been rendered into Chinese by Matteo Ricci and Xu Guangqi in 1607. A great number of mathematical terms used in Chinese today were first coined by Li. He discovered the Li Shanlan’s Summation Formulae in 1867. Later he worked in the think tank of Zeng Guofan. In 1868, he began to teach in Tongwen Guan.