A naturalised Spanish citizen, Alluni has maintained his innocence against charges of links to key al-Qaida suspects - including Mamoun Darkazanli, believed to be the organisation's financier in Europe.
After being initially released under supervision because he suffers from heart problems, Alluni was detained once more on 16 September as authorities were worried he might flee Spain after being denied permission to leave the country to attend his mother's funeral in Syria.
The verdicts in the mammoth trial, in which investigators pored over 130 hours and 39 minutes of evidence collated on 18 DVDs, are expected at 11:30 GMT on Monday.
The trial opened on 22 April and has heard testimony from 107 witnesses, including Jamel Zougam, a Moroccan alleged to be an acquaintance of Abu Dahdah, who is a prime suspect in the Madrid train bombings in March 2004.
Speaking from Madrid, Aljazeera chief editor Ahmed al-Sheikh said he hoped the verdict on Monday would reflect a Spanish police investigation that cleared Syrian-born Alluni of all charges except interviewing al-Qaida leader Usama bin Ladin in 2001.
Alluni insists he was doing his job as a journalist by interviewing bin Ladin.
But al-Sheikh said he feared the case was politically motivated. "From the very outset, the case was linked to what is known as the war on terror," he said.
"At the time, Spanish Prime Minister Aznar was well known for his close connections to the US."