Alfred Kleiner (24 April 1849 – 3 July 1916) was a Swiss physicist and Professor of Experimental Physics at the University of Zurich.

In the early 1890s, with his students Fritz Laager and Theordor Erismann, Kleiner conducted experiments to determine if changes in gravitational attraction could be caused by shielding.

At that time, most dissertations in physics by ETH students were carried out under the supervision of H.F. Weber, Einstein's former teacher at the Polytechnikum, as it was then called.

On 19 December 1901, Einstein writes to Marić that he had: spent the whole afternoon with Kleiner in Zurich and explained my ideas on the electrodynamics of moving bodies to him.

One year later he considered giving up his plan to obtain a doctorate and noted to his friend Michele Besso that "the whole comedy has become tiresome for me."

Einstein's earlier statistical physics papers (from 1902 to 1904) developed the foundations of a theoretical approach that he applied to concrete problems in 1905 and in subsequent years.

[3] In 1905 Einstein obtained his doctorate from the University of Zurich under Alfred Kleiner, with the thesis entitled Eine neue Bestimmung der Moleküldimensionen (A New Determination of the Molecular Dimensions).

On 7 May 1909 the Regierungsrat des Kantons Zürich appointed Einstein as an associate professor, effective from 15 October 1909, with a salary of 4,500 Swiss Francs per annum.