Their kidnappers, members of the Fatah movement, released the aid workers after being persuaded that their action would harm the Palestinian cause, a source involved the hostages' release said.
The two aid workers were the latest of several foreigners to be abducted in the Gaza Strip.
Palestinian armed groups usually carry out the kidnappings to demand money or wring concessions from the government.
Most foreigners kidnapped in Gaza this year have been freed unharmed within hours.
However, two journalists working for US-based Fox News who were abducted in August were held for two weeks before being released.
Fatah member shot
In a separate incident, Abdel Aziz Shahin, a former Palestinian cabinet minister from President Mahmoud Abbas's Fatah movement, was shot and wounded, sources from the group said.
An outspoken critic of the ruling Hamas government, Shahin was shot in the thigh as he left the office of a pro-Fatah radio station in Gaza City.
There have been no immediate claims of responsibility.
Gaza had been the scene of increasing violent conflict between rival Palestinian groups in recent months.