Oncken is a surname and may refer to:
- Arthur Oncken Lovejoy, a German-born American philosopher
- August Oncken (1844-1911), a German economist (German article)
- Hermann Oncken (1867-1945), a German historian
- Johann Gerhard Oncken (1800-1884), a pioneer German Baptist preacher
- Onno Oncken, a geologist
- Wilhelm Oncken (1835-1905), a German historian