Alexander Theodor von Middendorf (or Александр Федорович Миддендорф (for Russians)) (August 6, 1815 - January 16, 1894) was a Russian zoologist and explorer of Baltic-German origin.

Middendorf was born in Saint Petersburg, where he received his early education. He then studied for a medical degree at the University of Tartu, graduating in 1837. He undertook further studies at Berlin, Erlangen, Vienna and Breslau. In 1839 he became Assistant Professor of Zoology at Kiev. Shortly afterwards he took part in Karl Ernst von Baer's expedition to the Kola Peninsula.

From 1843 to 1845 he travelled to the Taimyr Peninsula on behalf of the St Petersburg Academy of Sciences. He published his findings in Reise in den äussersten Norden und Osten Sibiriens (Travels in the extreme north and east of Siberia) (1848-75), which included an account of the effects of permafrost on the spread of animals and plants. He also wrote Die Isepiptesen Russlands (1855), an account of bird migration in Russia.

He died at Hellenurme, Russian Empire (now in Valga County, Estonia).

Middendorff's Grasshopper Warbler , Middendorf's Cape (Novaya Zemlya), and Middendorf's Gulf (Taymyr Peninsula) are named after him.