The wire was taken from a section of the Auschwitz-Birkenau prison that was not protected for conservation, Polskie Radio reported.
Customs officials spotted the 12-inch-long wire when they inspected the man's luggage at Krakow's John Paul II airport.
The 66-year-old man said he removed the wire from a fence because his father had died at the camp during the war.
The camp, now a museum, has been subjected to several thefts in recent times.
In February, an Israeli couple received a three-year suspended sentence for stealing items from the site. In 2010, two Canadian teachers were charged with taking pieces from an unloading ramp. Their trial has twice been suspended.
In the most famous theft, a group of six men were sentenced to prison for stealing a sign that read "Arbeit Macht Frei" sign ("Work Makes You Free") in December 2009.