Bangladesh's Anti-Corruption Commission has filed charges against ex-PM Khaleda Zia's son, his wife and mother-in-law, officials say.
Mr Rahman has been in prison since March
They have been accused of acquiring their wealth illegally.
Businessman Tarique Rahman has been charged with amassing 48 million takas ($711,530) that did not match his legally declared income.
The authorities say the charges against him are part of a drive against corruption. He denies any wrongdoing.
Correspondents say the charges filed against him are far more serious than those filed by police in March, in which he was accused of extorting $147,000 from a construction company.
Mr Rahman's wife and her mother have also been charged with aiding him, commission official Zahurul Huda told the AFP news agency.
They face stiff jail terms and fines if convicted.
Mr Rahman, 40, is the joint secretary general of Ms Zia's Bangladesh Nationalist Party and was widely tipped to succeed her before his arrest and imprisonment in March.
Ms Zia and another son, Arafat Rahman, are also in jail pending trial on corruption charges.
About 150 high-profile suspects - including politicians, civil servants and businesspeople - have been arrested on corruption charges since the military-backed caretaker government came to power in January.
They include Ms Zia's great rival, Sheikh Hasina, who is also a former prime minister and leader of the Awami League.
The interim government has vowed to rid the country of corruption before it allows elections to be held in 2008.
For many years Bangladesh was ranked as the world's most corrupt country by the Berlin-based anti-corruption watchdog, Transparency International, but it is now no longer bottom of the list.