Baron Franz Xaver von Zach (Franz Xaver Freiherr von Zach) (June 4, 1754–September 2, 1832) was a German astronomer born at Pest in Hungary.

He served for some time in the Austrian army, and afterwards lived in London from 1783 to 1786 as tutor in the house of the Saxon minister, Count Brühl. In 1786 he was appointed by Ernest II, Duke of Saxe-Gotha-Altenburg director of the new observatory on Seeberg hill at Gotha, which was finished in 1791. At the close of the 18th century, he organised a group of twenty-four astronomers to prepare for a systematic search for the "missing planet" predicted by the Titius-Bode law between Mars and Jupiter. Ceres was discovered by accident just as the search was getting underway. From 1806 Zach accompanied the duke's widow on her travels in the south of Europe. He died in Paris in 1832.

Zach published Tables of the Sun (Gotha, 1792; new and improved edition, ibid., 1804), and numerous papers on geographical subjects, particularly on the geographical positions of many towns and places, which he determined on his travels with a sextant.

His principal importance was, however, as editor of three scientific journals of great value: Allgemeine Geographische Ephemeriden (4 vols., Gotha, 1798-1799), Monatliche Correspondenz zur Beförderung der Erd- und Himmels-Kunde (28 vols., Gotha, 1800-1813, from 1807 edited by Bernhard von Lindenau), and (Genoa, 1818-1826, 14 vols., and one number of the 15th, the suppression of which was instigated by the Jesuits).

He was elected a member of the Royal Swedish Academy of Sciences in 1794.

Asteroid 999 Zachia and the crater Zach on the Moon are named after him, while asteroid 64 Angelina is named after an astronomical station he set up near Marseille.