(Adds BMO lending rate cut)
TORONTO, Jan 27 (Reuters) - Royal Bank of Canada, the country's biggest lender, said on Tuesday it would cut its prime lending rate by 15 basis points, becoming the first of Canada's big banks to trim borrowing costs nearly a week after the central bank stunned markets with a rate cut.
Bank of Montreal, Canada's fourth-largest bank, quickly followed suit.
The moves by RBC and BMO take their prime rates to 2.85 percent from 3 percent, effective Wednesday, the banks said.
Canada's biggest banks, which also include Toronto-Dominion Bank, Bank of Nova Scotia, Canadian Imperial Bank of Commerce and National Bank of Canada, have come under fire for not immediately cutting their lending rates after the central bank's rate cut.
By not passing on the full rate cut to borrowers, the banks can protect their net interest margin, which boosts profits.
Typically, once one bank cuts its prime rate, the others follow in order to remain competitive with borrowers.
The Bank of Canada surprised markets with its Jan. 21 decision to cut overnight borrowing costs by a quarter of a percentage point, to 0.75 percent, to counter the effects of cheaper oil on economic growth and inflation. (Reporting by Andrea Hopkins and Alastair Sharp; Editing by Dan Grebler)