The prefecture of the Bas-Rhin region said in a statement the heavy memorial stone was discovered moved from its base Saturday morning.
Strasbourg mayor Roland Ries denounced “a new anti-Semitic act.”
“Anti-Semitism undermines the values of the Republic”, the prefecture said.
The monument commemorates a synagogue built in 1898 that was set on fire and razed to the ground by the Nazis in 1940.
The incident comes amid an uptick in anti-Semitic acts in France in recent months. Last month, about 80 gravestones were spray-painted with swastikas in a Jewish cemetery close to Strasbourg.