She ruled the country twice as Prime Minister since 1991. Zia was arrested in September last in connection with a graft case by the current military-backed caretaker government.
Last week, the high court granted her the bail in two scam cases clearing all legal impediments to her freedom.
Ms Zia was detained in a makeshift jail in parliament building complex. After being released, she went to the grave of her husband, slain president Gen Ziaur Rahman, to offer prayers.
Earlier, the former prime ministers's two sons--Tarique Rahman and Arafat Rahman-- arrested in connections with several scam cases were also freed on health grounds.