The Naturalization Act of 1906 was an act of the United States Congress signed into law by Theodore Roosevelt that revised the law from 1870 and required immigrants to learn English in order to become naturalized citizens. The bill was passed on June 29, 1906, and took effect September 27, 1906. It was modified by the Immigration Act of 1990.

The creation of the Bureau of Immigration and Naturalization (INS) under the Act provided for the first uniform naturalization laws in the country. Prior to 1906, an alien could be naturalized in any U.S. "court of record." After September 26, 1906, naturalization could only be done in courts having a seal and a clerk, and exerting universal competence.

The Act established standardized naturalization forms, requiring, inter alia:
• verification of arrival
• names and details of wives and children

In addition, section 15 of the Act defined the power of U.S. district attorneys to institute denaturalization proceedings: “in any court having jurisdiction to naturalize aliens for the purpose of setting aside and canceling the certificate of citizenship on the ground of fraud or on the ground that such certificate of citizenship was illegally procured