The 56-year-old avant-garde artist, who is not allowed to leave China, is represented at the festival by an empty chair that he designed himself in an ironic reference to his inability to attend.
"I feel sorry I can't come. That's why I have designed and sent something symbolic," he said in a pre-recorded video message broadcast at a press conference.
"I hope it can give some kind of statement on the way authorities can limit freedom of speech, can limit basic human rights for artists to travel or participate in cultural activities -- very ruthlessly and with no explanation."
His Ming Dynasty style chair -- shipped from Beijing for the 12-day event -- sat conspicuously between the other jury members in front of a cinema screen bearing the burly artist's bearded and somewhat haggard image.
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The chair had one quirky addition: a curved bar preventing anyone from sitting on it.
Ai, known as much for his human rights activism as his art, was detained for 81 days in 2011 during a roundup of activists, and was accused of massive tax fraud.
He was one of many government critics who were jailed or detained or disappeared into police custody in early 2011, when calls for anti-government protests in China -- echoing those during the Arab Spring revolts -- rattled the authorities.