The bank made 729 million riyals ($194.4 million) in the three months to Sept. 30, down from 899 million riyals in the same period of 2015, it said in a bourse filing.
Five analysts polled by Reuters had on average forecast the bank's quarterly profit would be 1.05 billion riyals.
The bank cited a 16.3 percent jump in total operating expenses, as general costs and impairment charges for investments rose.
It was the fifth quarter in the last six in which Riyad Bank reported either declining or flat profits.
Operating income for the third quarter was flat on the corresponding period of 2015 at 1.86 billion riyals, while profits from special commissions increased 4.8 percent to 1.32 billion riyals.
Loans and advances at the end of September stood at 152.6 billion riyals, gaining 10.2 percent on the same point of 2015, while deposits dipped 0.2 percent to 160.8 billion riyals.
The bank made 729 million riyals ($194.4 million) in the three months to Sept. 30, down from 899 million riyals in the same period of 2015, it said in a bourse filing.
Riyad Bank, Saudi Arabia's fourth-largest lender by assets, posted an 18.9 percent fall in third-quarter net profit on Tuesday, missing analysts' forecasts as costs rose.