John Hansel was stripped of citizenship by a federal court in Des Moines, Iowa, at the request of the US Department of Justice.
The prosecution charges the 80-year-old Hansl, with serving as a guard in the infamous concentration camp of Sachsenhausen near Berlin in 1943, and in the Natzweiler camp in France in 1944.
Thousands of political prisoners, Jews and civilians were imprisoned and killed in the two camps.
Ethnic German, Hansl was born in 1925 in what is now Croatia. In 1943, at the age of 18, he was called to join the SS. He admitted having been a guard at Sachsenhausen and later having been transferred to the front, where he was captured by the Allies.
He entered the USA with his family in 1955 on a visa obtained in Salzburg, Austria.
The trial of Hansl is the result of an investigation by the Office for Special Investigations of the US Department of Justice, which searches for former Nazis hiding in the USA.