PSNI detectives investigating the abduction and murder of Jean McConville in 1972 arrested a 57-year-old woman in west Belfast this morning.
The suspect has been taken to the Serious Crime Suite at Antrim police station for questioning.
Last week a 56-year-old man was detained by detectives investigating the murder of the Belfast mother-of-10 more than 40 years ago. He was later released.
The abduction, murder and secret burial of Ms McConville in 1972 is one of the most notorious incidents of the Troubles.
Veteran republican, 77-year-old Ivor Bell, was charged last month in connection with the killing. Mr Bell, from Ramoan Gardens in west Belfast, faces counts of aiding and abetting the murder and of IRA membership.
Ms McConville, a widow, was dragged away from her children in her home in the Divis Flats by an IRA gang of up to 12 men and women after being accused of passing information to the British army in Belfast.
An investigation later carried out by the Northern Ireland Police Ombudsman rejected the informer allegations.
Ms McConville was shot in the back of the head and buried 50 miles from her home. The IRA did not admit her murder until 1999, when information was passed on to gardaí.
She became one of the so-called Disappeared, and it was not until August 2003 that her remains were eventually found on Shelling Hill beach, Co Louth.