Janszoon, sometimes abbreviated to Jansz, is a Dutch patronymic surname, meaning "son of Jan". People with this name or its variants include:
Aart Jansz Druyvesteyn (1577–1627), Dutch Golden Age painterAnthonie Jansz. van der Croos (1606–1662), Dutch painterAnthony Janszoon van Salee (1607–1676), original settler of and prominent, wealthy landholder, merchant, and creditor in New NetherlandClaes Jansz. Visscher, (1587–1652), Flemish draughtsman, engraver, printmaker and publisherDiederik Jansz. Graeff, (1532–1589), first illustrious member of the De Graeff family, a rich merchant, Ship-owner and PoliticianDirk Jansz Smient, governor of Mauritius in the new settlement at Grand Port from 1666 to 1669, when he returned to Cape of Good HopeErnst Jansz (born 1948), one of the founding members and frontmen of Doe MaarFrederica Jansz, Sri Lankan Burgher journalist, Editor of the Sunday LeaderGeoff Jansz (born 1958), Sri Lankan Australian Burgher chef and television presenterJacob Jansz. Coeman (born after 1676), Dutch painter of the 17th centuryJan Jansz. Weltevree (born 1595), Dutch sailor and probably the first Dutchman to visit KoreaJan Jansz de Jonge Stampioen (1610–1690), Dutch mathematician famous for his published work on spherical trigonometryJan Janszoon, (1570–1641), first President and Grand Admiral of the Corsair Republic of Salè, Governor of Oualidia, and a Dutch pirateJan Janssonius, (1588–1664), also known as Jan Janszoon, Dutch cartographerJan Janszoon de Heem (1650–1695), Dutch Golden Age still-life painterJob Janszoon van Meekeren (1611–1666), Dutch surgeonLaurens Janszoon Coster (1370–1440), the inventor of the printing press from HaarlemLenaert Jansz de Graeff (1530–1578), son of Jan Pietersz Graeff, a rich cloth merchant from AmsterdamLucas Janszoon Waghenaer (1533–1606), Dutch chief officer and cartographerMichiel Jansz. van Mierevelt, (1567–1641), Dutch Golden Age painterNeville Jansz, Sri Lankan Burgher civil servant and diplomatPieter Jansz. Saenredam (1597–1665), painter of the Dutch Golden AgePieter Jansz van Asch (1603–1678), Dutch Golden Age painterSalomon Jansz van den Tempel (1633–1673), 17th-century master shipbuilderWillem Janszoon (1570–1630), Dutch navigator and colonial governor, is the first European known to have seen the coast of Australia