Karl Wilhelm von Nageli (March 27, 1817 - May 11, 1891) was a Swiss botanist.

Nageli was born near Zurich. He studied botany under Augustin Pyrame de Candolle at Geneva, and graduated with a botanical thesis at Zurich in 1840. His attention having been directed by Matthias Jakob Schleiden, then professor of botany at Jena, to the microscopical study of plants, he engaged more particularly in that branch of research. Soon after graduation he became Privaldozent and subsequently professor extraordinary, in the university of Zurich; in 1852 he was called to fill the chair of botany in the university of Freiburg-in Breisgau ; and in 1857 he was promoted to Munich, where he remained as professor until his death.

Among his more important contributions to science were a series of papers in the Zeitschrift fur wissenschaftliche Botanik (1844 1846); Die neuern Algensysteme (1847); Gattungen einzelliger Algen (1849); Pftanzenphysiologische Untersuchungen (1855 1858), with C. E. Cramer ; Beitrage zur wissenschaftlichen Botanik (1858-1868); a number of papers contributed to the Royal Bavarian Academy of Sciences , forming three volumes of Botanische Mitteilungen (1861-1881); and, finally, his volume, Mechanisch-physiologische Theorie der Abstammungslehre, published in 1884.

The standard botanical author abbreviation Nägeli is applied to species he described.