Samir al-Qadi, from Hebron, was arrested on June 16, 2011 and Rahman Zeidan from Tulkarem was detained on June 2, Addameer said.
Both officials are elected Hamas lawmakers.
On Thursday, Israel extended the administrative detention of Muhammad Natsheh for four months. He was arrested by Israeli forces on Jan 31.
There are at least 210 administrative detainees being held in Israeli jails, including 5 members of the Palestinian Legislative Council, according to Addameer.