By Mark Dummett
BBC News, Dhaka
Mr Nizami was a minister in the former government
The leader of Bangladesh's largest religious party has been held in the government's anti-corruption drive.
Jamaat-e-Islami chief Motiur Rahman Nizami, who was in the cabinet of the government led by Khaleda Zia, has denied the charges.
Ms Zia is one of the two former Bangladeshi PMs among more than 100 politicians already detained on various corruption charges.
A court has charged former PM Sheikh Hasina in a separate graft case.
Bangladesh's army-backed interim government has promised to clean up the country's murky political scene, and 18 months after it took power, shows no sign of letting up.
The police seized Mr Nizami, the head of the largest Islamic party, from his house at around midnight on Sunday, despite a thunder storm and the presence of several hundred of his angry supporters.
Earlier on Sunday police arrested two of Mr Nizami's fellow former ministers, and a court charged another former prime minister Sheikh Hasina in a separate graft case.
Mr Nizami is one of the most important conservative religious figures in Bangladesh.
He has said that the charges are politically motivated.
He is alleged to have benefited from the illegal awarding of business contracts, when Jamaat-e-Islami was a coalition partner of the Bangladesh Nationalist Party of Khaleda Zia.
The police accuse her, one of her sons, and 22 others, including 11 former ministers of involvement in the illegal deals.
They all say they are innocent.
The military-backed government has promised to restore democracy by the end of the year, but its not clear who will lead the main political parties into the elections, as most prominent politicians are now behind bars.