The banking group, 70% owned by the taxpayer, registered a pre-tax loss of £2.2bn for the three months to 30 September compared with a profit of £1.9bn in the same period last year.
The firm says it wrote off £3.3bn in bad debts in the quarter.
Excluding the losses, group operating profit rose 55% to £1.75bn.
Stephen Hester, chief executive of RBS says the results demonstate the “headwinds” the group still faces but he remains confident the bank will recover in the long-term.
Earlier this week, RBS announced it was to sell some of its brands and 318 branches.
RBS will dispose of branches in England and Wales, which originally operated under the Williams & Glyn’s brand until the 80s as well as selling off its NatWest brand in Scotland.
It will also sell its RBS Insurance portfolio, which includes the Direct Line, Churchill and Privilege brands and card payment business Global Merchant Services.
The move follows pressure from European competition commissioner Neelie Kroes, who demanded RBS sell some of their operations follwing its bail-out by the Government last year.