János Sajnovics de Tordas et Káloz (1733, Tordas – 1785, Pest) was a Hungarian linguist and Jesuit. He is best known for his pioneering work in comparative linguistics, particularly his systematic demonstratation of the relationship between Sami and Hungarian.
Sajnovics was a pupil of the astronomer and mathematician Maximilian Hell. When Hell planned an expedition to observe the transit of Venus in Vardø, northern Norway in June, 1769, he took Sajnovics with him. Hell had heard that the Hungarian and Lapp (Sami) languages were related and thought that Sajnovics, as a native Hungarian speaker, would be able to investigate the connection.
Sajnovics published the results of his research in his Demonstratio idioma Hungarorum et Lapporum idem esse (1770), which was a breakthrough in the study of Uralic languages. Sajnovics's ideas were further developed by Samuel Gyarmathi.