Alleged ringleader Ali Umari and Muhammad al-Jundi were accused by the state security court of "plotting to carry out terrorist activities" in Israel and against tourists in Jordan.
Three other defendants were given reduced sentences for seeking to recruit fighters to train in Syria and Lebanon, an offence the prosecution said was a plot to undermine Jordan's ties with a foreign country.
Another defendant, Abd al-Muti Abu Muiliq, was sentenced in absentia to five years for the same offence. Thought to be hiding in Syria, he had already been sentenced to death in 1997 for assassinating a Jordanian diplomat in Beirut in 1995.
Two defendants were acquited in the trial, which opened in May.
A defence lawyer said he would appeal the convictions.
The suspects told the court in June that they made their confessions under duress and denied the charges against them.
According to the charge sheet, the eight defendants began meeting in November 2004 to plot attacks against tourists in the northern Jordanian cities of Irbid and al-Husn.