Frederik Kaiser (Amsterdam, June 10, 1808 – Leiden, July 28, 1872) was a Dutch astronomer. He was director of the Leiden Observatory from 1838 until his death.

He is credited with the advancement of Dutch astronomy through his scientific contributions of positional measurements, his popularization of astronomy in the Netherlands, and by helping to build a state - of - the - art observatory in 1861 (Today it is known as the "Old Observatory".).

He made a series of drawings of Mars at its opposition in 1862 and made a fairly precise determination of its rotational period.

Craters on Mars and on the Moon are named in his honour, as well as asteroid 1694 Kaiser.

In Richard Proctor's now abandoned Martian nomenclature, Syrtis Major Planum was called the "Kaiser Sea". This nomenclature was later dropped in favor of the one introduced by Giovanni Schiaparelli.