The official Saudi Press Agency (SPA) released photographs of eight airmen it said were involved in yesterday's US-led operation, carried out with Gulf allies.
In one picture they stood, some smiling, in green flight suits with arms around each other in front of one of their fighter jets.
One of the pilots involved in the raids is a son of Crown Prince Salman bin Abdul Aziz himself, according to Saudi newspapers.
One Twitter user said the air force men were "wanted by IS" while another said their throats "will sooner or later be slit".
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A broader threat came from a Twitter post which called for the killing of police as well as military men.
Some Internet users, however, defended the Saudi airmen.
"The Saudi pilots returned safe and sound yesterday morning after having accomplished their duty in carrying out successful and effective strikes against the Islamic State extremist organisation in Syria," SPA said overnight.
"My sons, the pilots, fulfilled their obligation toward their religion, their homeland and their king," SPA quoted Crown Prince Salman as saying.
He was "proud of the professionalism and bravery" of the Saudi air force men, SPA said.
Their combat mission happened to coincide with the kingdom's 84th national day.
Saudi Arabia is dominated by the ultra-conservative Sunni doctrine of Wahabism.
The kingdom's Grand Mufti Sheikh Abdul Aziz al-Sheikh last month said Al-Qaeda and the IS group "have nothing to do with Islam and (their proponents) are the enemy number one of Islam".