The kingdom's benchmark slips 0.5 percent to 7,702 points. It reached its highest close since April 2012 on Sunday.
Shares in Yanbu National Petrochemical Co (Yansab) decline 2.2 percent to 56.5 riyals ($15.07).
Yansab's second-quarter net profit rose 3.2 percent to 671 million riyals ($179 million). Analysts on average forecast the company would make a quarterly profit of 708.65 million riyals.
"We reiterate our 'hold' recommendation on the stock with a fair value of 59.30 riyals per share," Ankit Gupta, assistant vice president of research at NBK Capital says in a note. "We believe that Q2 results underscore company's operational resilience; however, it is mostly priced in the stock."
Saudi Basic Industries Corp (SABIC), Yansab's parent firm, also slips, losing 0.5 percent.
Saudi Arabian Fertilizer Co (Safco) retreats 0.3 percent after its earnings also trailed analysts' forecasts.
Elsewhere, UAE markets extend gains as investors buy ahead of corporate results. Dubai's index advances 0.5 percent to 2,452 points and Abu Dhabi's measure climbs 0.5 percent to 3,758 points.
Dubai-listed budget carrier Air Arabia climbs 6 percent.
Oman's benchmark rises 0.7 percent to 6,564 points, a four-week high.