Robert Mardini, head of Red Cross operations for the Near and Middle East, said the four were "safe and sound" after their abduction on Sunday.
ICRC spokesman Ewan Watson said they had been released in the Idlib region, a near-lawless area in northeast Syria where hundreds of militia operate, but did not elaborate on the circumstances.
The ICRC was awaiting information on the remaining three, he said.
The six Red Cross workers and local Red Crescent volunteer were abducted by gunmen as they were returning to Damascus after a four-day mission to deliver medical supplies.
The Syrian Observatory for Human Rights, which monitors violence in Syria through a network of activists and military sources, said the abducted staff had been captured by the al Qaeda-linked Islamic State of Iraq and the Levant and that several rebels from another group were taken with them.
Mr Mardini said the ICRC remained committed to its relief operations in Syria where it was delivering food, water and medical supplies to displaced civilians.