Abu Dujana was arrested in June on charges of "keeping explosives and sheltering fugitives wanted for a series of deadly attacks" in the country in recent years.
The chief judge of the south Jakarta court, Wahjono, said Dujana had been sentenced to 15 years for rifles and ammunition possession and funding and harbouring other group members.
Dujana has denied any role in attacks blamed on JI, which the panel of three judges said was a "terrorist" organisation.
Indonesian authorities say they cannot ban the group since it is not a formally established organisation.
Indonesia is the world's most populous Muslim country.
Last Mod: 21 Nisan 2008, 15:17