The bank made 851 million riyals ($226.9 million) in the three months to Dec. 31, down from 1.06 billion riyals in the same period of 2014, according to a bourse statement.
It cited for the profit drop lower operating income, smaller gains for non-trading investments and reduced fee and commission income, as well as a 12.5 percent rise in operating expenses.
Five analysts polled by Reuters had on average forecast the bank's quarterly profit would be 850.5 million riyals.
Saudi companies issue brief earnings statements early in the reporting period before publishing more detailed results later.
Operating income for the fourth quarter fell by 4.4 percent on the corresponding period of 2014 to 1.91 billion riyals, while profits from special commissions increased 1.3 percent over the same timeframe to 1.35 billion riyals.
Riyad Bank has been weighed down in recent quarters by higher provisioning and a rate of loan growth below the average for the sector. It reported lower profits in the previous two quarters, ending a run of at least 14 consecutive quarters of earnings growth.
The kingdom's banks have been adjusting to more tepid operating conditions since last year as a result of lower oil prices.
Loans and advances at the end of December stood at 144.7 billion riyals, gaining 8.4 percent on the same point of 2014, while deposits edged up 1.8 percent to 167.09 billion riyals over the same period.