Thaksin and his wife Pojaman are due to appear in court on Tuesday to face charges of abuse of power and conflict of interest in the purchase of prime Bangkok real estate when he was in office.
Thaksin and Pojaman have been charged with malfeasance and conflict of interest for the 2003 purchase of a plot of land in central Bangkok from a government agency.
An anti-corruption law bars prime ministers and their spouses from doing business with government agencies, but there is some dispute over whether the law applies in this case because the agency that sold the land was not technically under the authority of the prime minister.
The couple have pleaded not guilty.
Thaksin was toppled in a 2006 military coup faces other court action on similar charges.
His allies won elections last December, paving the way for him to return
from exile in February, vowing to clear his name after opponents accused him of corruption and destroying Thai democracy.