An Israeli military court has convicted the Speaker of the Palestinian parliament of being a member and officer of an illegal organisation.
Abdel Aziz Dweik belongs to the Hamas movement, which controls Gaza.
He has been in prison since his arrest by Israeli forces in 2006 and will be sentenced at a later date.
Dozens of Palestinian legislators were arrested by the Israeli army in 2006. Thirty lawmakers remain in Israeli custody.
They were detained following the capture by Hamas-allied militants of an Israeli soldier, Gilad Shalit.
Israel has outlawed Hamas and Israeli courts have so far convicted 10 legislators of membership of the Islamist group.
Typically the sentence for these offences is between six months and three years.
Gilad Shalit remains in the militants' custody.