Earlier, four Tornado GR4s - armed with Paveway IV guided bombs and precision-guided Brimstone missiles - took off from Akrotiri base in Cyprus.
Sky's Defence Correspondent Alistair Bunkall said the first missions were launched "barely an hour" after MPs backed airstrikes by a majority of 174.
"The target was an oilfield held by Islamic State in the east of Syria," he said. "This is a show of intent from the Government.
"Clearly they had some pre-planned targets ready to go if the vote was a yes ... they did not want to hang around."
The Tornados are a small but significant addition to the coalition strike force in Syria and more aircraft will soon be joining them from the UK.
Six typhoon jets from RAF Lossiemouth are expected to head to Cyprus along with more Tornados from RAF Marham in Norfolk.
Their British-designed Brimstone missiles are a vital asset, with the ability to hit targets with remarkable accuracy and limit collateral damage.
US President Barack Obama welcomed the UK's vote agreeing to expand military action against IS - saying it demonstrated the coalition's "unity and resolve".
On Wednesday night, MPs voted by 397 to 223 in favour of extending British action against IS - also known as ISIS, ISIL and Daesh - from Iraq into its Syrian stronghold.
The margin of victory was larger than most had predicted.