Karl-Friedrich Bonhoeffer (13 January 1899 – 15 May 1957) was a German chemist.

Born in Breslau, he was an older brother of martyred theologian Dietrich Bonhoeffer. His father was neurologist Karl Bonhoeffer and his mother was Paula von Hase.

Bonhoeffer studied from 1918 in Tübingen and Berlin, finishing his PhD in 1922 in Berlin with Walther Nernst. From 1923 to 1930 he was an assistant with Fritz Haber at Kaiser Wilhelm Institute for Physical Chemistry and Elektrochemistry in Berlin Dahlem. After the Habilitation in 1927, he became full professor at the University of Berlin. In 1930, Bonhoeffer was appointed a professor of Physical Chemistry at the University of Frankfurt. Four years later, he was appointed a professor of Physical Chemistry at the University of Leipzig.

In 1935, he was refused permission by the Reich Minister of Education Bernhard Rust to attend a Kaiser Wilhelm Society memorial for Fritz Haber, the "father of chemical warfare", who had died in exile after refusing to expel Jewish scientists from the Kaiser Wilhelm Institute for Physical Chemistry. This was the only organised public protest by scientists in Nazi Germany.

Soon after the isolation of heavy water through electrolysis by Gilbert N. Lewis in the United States in 1933, Bonhoeffer suggested the production of heavy water to the Norwegian company Hydro, part-owned by IG Farben from 1927, and the process was launched in 1934. His Leipzig assistant Karl Wirtz also worked on heavy water at the time.

By February 1940, together with his friend and colleague Paul Harteck he was among the recipients of Werner Heisenberg's early report on the building of a nuclear weapon. He and Wirtz then discussed the production of heavy water as a neutron moderator for the projected bomb with the Army Ordnance (Heereswaffenamt, HWA) in Berlin, and he managed to interest Paul Herold at IG Farben in testing catalytic conversion as a more economically viable alternative to electrolysis.

In January 1942, he and Heisenberg personally intervened in Berlin, using the Wehrmacht connections of his brother-in-law, Gerhard Leibholz [de], to obtain exemptions (Unabkömmlichstellung) from the military service call-up for Harteck and Carl Friedrich von Weizsäcker as core members of the German nuclear programme. In February 1942, he attended a conference on the industrial production of heavy water through catalytic conversion at the Kaiser Wilhelm Institute for Physics in Berlin with Harteck, Hans Suess and Paul Herold of IG Farben. With the Nazi government reserving large expenses for its war effort, IG Farben was subsequently contracted by HWA to build the plant in return for a share in patent rights on nuclear power. In late September 1943, having faced repeated Allied sabotage of Norwegian heavy water production, Bonhoeffer held a meeting to discuss IG Farben's financial demands, together with Kurt Diebner and Harteck, as a heavy water pilot plant in Germany was nearing completion. The plant was abandoned due to its excessive price tag, and Bonhoeffer's student Herbert Hoyer experimented with an exchange process facilitated by bacteria.

He survived the British air raid on Leipzig in December 1943.