Karl Wilhelm Valentiner (22 February 1845 in Eckernförde – 1 April 1931) was a German astronomer.

In 1874, Wilhelm Valentiner led a successful German expedition to Zhifu (China) to observe a solar eclipse.

Since the observing conditions in the Mannheim city centre were deteriorating, Grand Duke Frederick I of Baden approved Valentiner's request to relocate the observatory in Karlsruhe in 1880.

Much to the annoyance of Valentiner, now appointed Professor of the University of Karlsruhe, no new observatory was built.

After the establishment of the "Grand Duchy Mountain Observatory" (today's Heidelberg-Königstuhl State Observatory) in the year 1898 Valentiner was placed over the Department of Astrometry, which stood in competition with the Astrophysics Department under Max Wolf.